I watched his review show yesterday and noticed that his mouth was crooked and was totally more noticable whenever he spoke...did he have a stroke or something?

He had surgery a few weeks ago. Ebert has papillary (thyroid) cancer, a common (and curable) type.
From a post in tvtalk.

So who will set across the aisle from Roeper when Ebert bites it?

Well hopefully he wont bite it.. though I would think that some will suggest this is the reason why he has "lost it" for most of his reccent reviews now a days.