I thought I'd try to ease the distress of all the Wilson fans here after those Season 5 promos par giving toi my well-funded reason why Wilson can't leave:

if Wilson leaves, the effects on House would simply be disastrous... it's like action and reaction:

The things that make House who he is apart from his brilliance and his gift are his constant self-destructive behaviors (interesting and intriguing), his drug habit and his obvious talent for insulting and mocking other's with great credibility. Those are also the things that give him an edge on all the other doctors on TV and the reasons House needed Wilson to save him before either got him in trouble...

so Wilson quits... how does House go on without him?

A: He continues as if nothing has happened: eventually ends up on a bad jour with nothing to distract him from his leg and makes a stupid decision, loses his doctor's license because of his pills ou insults the wrong person without a safety net...
Results in: death ou jail, either way the montrer can't go on.

B: He stops self-destructing, gets clean, stops insulting people... he...blends in with the other doctor's on TV!? (his brilliance would still remain, of course but with such a dramatic change his way of thinking would be in danger too so maybe... he'd even lose that.)

HOUSE? BLENDING IN? NO. NEVER...

He is popular, the montrer is populaire because he sticks out like a sore thumb amongst your normal doctors.
Results in: A lesser House and a lesser show... not to mention that a depressed House without his normal outlets can get some pretty wrong ideas. (the drugs can go, the insults can go, but the pain remains...)

OR:

C: Wilson returns, House gives him respect without falling out of character... and House's spirits might lighten a bit, not very drastic, but he might try to take better care of himself; might try to give back some plus in a very House-like way.

and IF in that, he tries to get off of the vicodin... then in my opinion he's addicted to not being in pain: his motive for ever starting on the vicodin was pain, never curiosity, never wanting to be high... he started purely to get rid of the pain. any drug that get help him get rid of the pain could be his new addiction... and whilst wanting to be high ou numb all the time is somewhat unnatural, no shrink would ever try to convince toi that not wanting to be in pain is abnormal... so I don't really know if there would be any sense in trying to talk him out of it... Even though the cause of his elevated pain levels can sometimes be psychological. Maybe if he Lost his automatic reflex to pain (which is pill), the addiction wouldn't be such a problem. (that would require a shrink too but maybe House would be so apt on keeping Wilson beside him that he would just do that.)
Results in: The montrer as we know it:with Wilson and of course fantastic!

and a short last note about the rumors that Cuddy might get her own spin-off: She is House's boss... he is still employed because she saves him all the time: if she left there would be another dean of medicine... a less forgiving one:
House is... himself, gets fired... end of show.

Wilson and Cuddy are the foundation of House: they fuel the 2 most interesting sides of him... they can't go anywhere.

That's about it.

Thanks for reading!