Gross medical question!

I saw a car crash victim's tongue reattached in a documentary once. So yes, it can. As far as speaking properly, I don't remember.

Maybe you can make it a "Beware of who you're talking about" thread

You'd want to talk to an ENT specialist to be sure, but virtually any organ with at least medium sized vessels CAN be reattatched assuming it is still viable. I'd imagine that for a tongue that would mean within a few hours and something severed would be in better condition than something that had been avulsed. The tongue also has both central and peripheral nerve innervation so (again a guess, talk to a speech pathologist as well) probably there'd be some return of speach but I wouldn't be surprised at some sort of permanent identifiable problem with certain sounds and letters