( I know this is long but if you take the time to read it I think you might like what I laid out)
I personally don't think any of them need to come back, and have plenty of faith in the current roster. I think the only way that any of them should be used is to in turn make something really really big happen. Not that their returns wouldn't be big enough as is, but it's not really necessary. If your going to do it I would use The Rock if you could pay him enough money to wrestle for a while, and I would bring in Goldberg for a little while as well. I'll say 6 months.
I would use The Rock to turn John Cena. I think that is going to be a serious shit your pants moment when this guy turns heel at some point, and don't think he won't. The returning Rock would have huge fan support and be able to instigate a feud with Cena. You could have The Rock come out for his welcome back ceremony where he would bring people up to speed telling everyone he is going to be back for awhile in more words or less. From here he could go on a rant about why he's coming back, have him say something about the WWE going soft, and needing someone to come and stick their boot sideways up someone else's roody poo candy ass, because that's not what The Rock has been seeing going on around the WWE lately!!!
This next part is where he instigates the feud. The Rock then just shoots on Cena, the usual criticisms and then some delivered fashionably by The Rock. He would have to make mention of how the crowd boos him all the time and how stupid he looks just smiling back at them like a kid on a sugar high, something along those lines.
This then prompts Cena to come out and do the "Why you hatin' dog, I respect you, I love the business, blah blah blah" promo, which the Rock interrupts with "IT Doesn't Matter What You Think!!!" or something like that, to which the crowd roars. The Rock says he's calling out John Cena to prove the difference between PG and TNT (i.e. dynamite)(analogy to that nature, He's back and John Cena is the guy The Rock wants to face to prove he is still the most electrifying man in sports entertainment, and prove that John Cena is (insert expletive, or some kind of derogatory terminology) totally dogging Cena the whole time to instigate the feud.
Cena then says that The Rock needs to shake off his ring rust before he thinks about getting in the ring with him, this is where we begin to see a little attitude coming from Cena where he is showing he is actually getting mad. As he continues to cut his own promo on The Rock he becomes more and more upset as he is speaking, showing that whatever was said got under his skin.
Cena says if The Rock can beat an opponent of his choosing then he will have a match with him at the next PPV in any style of match he wants. The Rock just stands there for a second as though he is thinking about it, letting the crowd get a little anxious, then slowly reaching out to shake on it with Cena who in turn slowly reaches out to shake hands, and that is the end of the initial segment to get this ball rolling.
Cena would then choose someone big like Randy Orton, Triple H, or Batista who The Rock would then beat in a the main event of the show.
The next week The Rock would reveal what type of match he wants to have saying that he is choosing a match he has had some experience in, an "I Quit" match, vowing to make Cena quit to much fan reaction. The Rock informs the crowd as well as Cena that the paperwork is ready to be signed, so later they would have a contract signing, where both men end up tough talking each other, cut their promos, and hype the match. No one touches anyone, no fights or hi-jinx, just tension.
The next week you could do something like have them be in a tag match or something, but neither ever gets a hold of the other man, once again they don't lock horns. Have them face whatever tag team you wish, they coexist and win the match, afterward staring each other down, ending the show.
The whole time you are seeing Cena get legitimately mad(kayfabe) once again as if he is about to lose control as the crowd chants Cena Sucks, and the Camera shows all the anti Cena signs possible, as The Rock shoots on him about all of that kind of stuff saying how much he sucks, calling him out on the 5 moves of death, FU and STFU, etc... which the fans would probably cheer coming from The Rock setting the stage for a Cena turn.
At the PPV the two would of course have the match and that can go almost however you can imagine an "I Quit" match between The Rock and John Cena going until the finish. Right before they decide to take it home, The Rock will get John Cena in his sharpshooter, Cena sells it like crack, and the fans get the feeling Cena is about to quit from the pain as The Rock keeps yelling at him asking if he's ready to quit. The Rock let's Cena out of the Sharpshooter and goes to get a mic after holding Cena in the move for a long time to try and get him to say "I Quit" in the microphone.
Cena is recovering and begins to get up as The Rock slides in the ring with the mic in hand rushing over giving Cena some Rock Punches with his free hand to which Cena starts to fire back with lefts and rights getting the upper hand to Irish whip The Rock into the ropes to hit his flying shoulder block beginning the 5 moves of death leading to the F-U. Cena then grabs the mic that had fallen out of The Rock's hand putting it too his face asking if he quits. The Rock refuses and Cena starts getting frustrated, now hovering over The Rock punching him in the face repeatedly asking is he wants to quit. Cena gets more and more viscous beginning to slam his head up and down on the mat completely freaking out trying to end The Rock.
Cena then goes and gets a chair repeatedly beating The Rock with the chair as the crowd boos him, to which Cena responds by going and getting the ring bell and hitting The Rock with it too, picking him up off the canvas to hit him with another F-U as well. After the next F-U The Rock finally says "I Quit" realizing he is too injured to win now. Afterwards Cena continues to beat The Rock, and mock the fans yelling at them seemingly cursing them, and freaking out the whole time.
It would then be the next night on Raw where Cena came out and said how he just let go during the match, and stopped caring what the crowd thought, and just wanted to beat The Rock. He says he's tired of trying to win them over only to have them constantly chant he sucks, much like they did to The Rock which is why he wanted to beat him, because he is better than The Rock ever was. Cena goes on to say "If I can't make you love me, Boy am I gonna make you hate me." and starts by just getting out of the ring right after saying that right over to Jerry Lawler to kick his ass which he does as the fans boo and chant against him, and you have finally turned Cena heel.
I apologize for the length but now that you've read it hopefully you understand why, I had to give details to make it make sense.
With Goldberg I would make have him feud against Batista in a feud much like he had with Triple H in HIAC matches to build Batista, keep in mind I would just be bringing both The Rock and Goldberg in to help establish the new generation as well as John Cena and Batista for maybe 6 months. Batista of course would come out on top of this feud, and it's one that at one time people were dying to see, and would probably still enjoy.
I see no real use for Sid, he just doesn't really have a place in the WWE anymore. In his prime he was a very intimidating specimen, and is still big, but I can't imagine that he could deliver a quality match any better than Goldberg at this point and between the two I'll take Goldberg.
Once again, sorry for the length if it was all that bad.
