Initially rehabilitation plays no part. Picard recognizes the bridge of the Enterprise within seconds of regaining consciousness . He doesn't speak to Will Riker as if he were someone he hadn't seen for thirty years. The "life experience" aspect of the alien download obviously begins to disappear immediately. Picard remembers elements of the story line he was exposed to, and is effect by it. But it's not like he personally lived thirty years off the ship and then return after that time.
O'Brien continues to remember the time he spent imprisoned personally, the impression I received from that episode is that it would remain with him as an actual event in his life always.
Picard realizes very quickly that the download wasn't real.
I'm not so sure. I mean, perhaps the readjustment might be lesser than say spending 30 years in a POW camp & being dropped back into your home
But still, it's clear that even a year later he still remembers the notes to the song he learned in that "20 minutes". He apparently recalls all of the people & events of that encounter as if it was a 30 year period of his life
Even that in itself would require some psychotherapy of some sort, even if to just cope with the grief of losing it & them. He is irrevocably altered from then on.