Odds are, the Undertaker/Kane (+2) vs Wyatt Foursome will still take place, probably between the semi-final matches and the final championship match on the card. So, those guys will likely not be involved in the tournament, which probably will just be 8 guys.
Reigns and Ambrose will both be in it. Probably Owens and Del Rio as well, as they were both in the 4-Way and are solid heels. I'd add Ziggler as well, but he might be tied up with Breeze, and, actually, Del Rio might be tied up with Swagger, unless they really want to just throw those guys in as well to make first round matches, Del Rio/Swagger and Ziggler/Breeze. Ambrose could face Owens and Reigns could face an eighth guy to round things out.
Reigns beats the TBD guy, probably Big Show. Ambrose goes over Owens. Del Rio over Swagger, and maybe Breeze over Ziggler.
Reigns over Del Rio. Ambrose over Breeze.
That sets up Reigns and Ambrose in finals. Reigns is the given. I'd be shocked if he doesn't make it that far. Ambrose is a little iffy, but judging that he really is the second pick of so many people to make it that far, how involved he is with Reigns, and the small hints of a heel turn, I can see the story unfolding in his favor. However, if they really want Reigns to win, they could just push one of the heels, Owens, Del Rio, or even Sheamus, through over Ambrose to get Roman a better face reaction.
This is Survivor Series though, and everyone is expecting a screwy finish to this tournament, much like everyone was expecting a screwy finish to Reigns/Rollins anyway. Some have been suggesting the Authority screws Ambrose, in the event of Ambrose/Reigns in finals, a match where Ambrose will likely be cheered at least in a 60/40 majority, and backs Roman Reigns to win his first WWE title. Much like 1998, we have a new, fresh, heel champion, and a big babyface in Ambrose to chase him.
However, the inverse is also possible. Assume the same match, but Ambrose turns instead. He sells out to win gold, citing jealousy of Roman's success, and Reigns remains the babyface to chase Ambrose into Mania. It could happen.