Does Jericho need the WWE anymore, no.
He is an established WWE Legend, future Hall of Famer (if it had NFL Rules he'd be '1st Ballot'), a bonafide rock star with successful tours and album sales, in the mainstream media he can be placed firmly in the C-D List (which aint bad for a wrestler with only one major motion picture).
Does WWE need Chris Jericho anymore, not necessarily.
They have their main eventers in place for now (Cena/Orton/Taker/Edge) and the next 5 years (CM Punk, Miz, Sheamus, Barrett). So Jericho who, while a great champion, was basically a 'spot starter' in the main event isn't really needed unless injury or worse insues. WWE has midcard talent (Rhodes, Bryan, Ziggler, Mysterio, Del Rio, DiBiase, and yes Santino) that, while Creative hasn't really helped always, can entertain in ring and on the mic. So Chris can only really be best utilized to make up for the deficencies in the writing room. Kinda below his pay grade in my opinion.
But because they (WWE/Jericho) don't need each other, it doesn't mean we don't need him.
There is a void there now that he is gone. It may not affect all of us but seriously, his last SD! run, he was a solid promo, could get everyone involved over, generated heat, and delivered in the ring, and never got seriously injured. He was the one person on that roster that you could put out there and not worry about.
Unlike Taker, Mysterio, and Edge (all injury prone); Swagger or MVP (can't connect with the crowd); CM Punk, Big Show, and Christian (seem to have all of 'it', but 'it' doesn't come together for some reason).
On NXT he was very instrumental for helping Wade Barrett get over. Besides the backstage help Barrett has praised him for, check out the commentary when Jericho had Wade replace him in the 'Pro vs. Rookie' tag match...amazing. His job as a manager ringside was great also, the way he'd interact with Josh Matthews while working the apron. He'd yell at Josh to mention how great Wade was after a move or counter. Every now and then the camera would catch the smile on his face as he was actually enjoying himself before they'd cut away.
On RAW...back to JeriShow, he was entertaining all of the time. The banned from RAW conspiracy theory, while not as classic as his WCW one back in the day was so much fun. He did get lost in the shuffle when he last had a RAW run, but thats because the show was too top heavy. He needed to stay on SD! then.
In closing, I think there is a lot left for Chris Jericho to accomplish in WWE. While he has won the World Title a few times since his '07 return, he hasn't won the WWE Title since he Unified them 7 or so year's ago. So a title run there would be awesome.
A U.S. Title run can accomplish a few things, help get the champ he beats to the next level by having some great matches, give him the one non-crusier title left for the taking (he's never been US Champ), and then put over another up-and-comer when dropping the title. I think CM Punk is the only one left on both roster's that are able/most likely willing to do such a thing.
He never won the Royal Rumble. That IMO is a travesty that meeds to be rectified.
And I feel he deserves a shot at Taker at Wrestlemainia, of course to lose. There are only a few Susperstars left that Taker hasn't faced that EARNED the privelige to go at 'Mainia. Chris Jericho heads that list. (Cena and Mysterio, surprisingly are the other two).