Yes, Gandalf would have rescued Gollum.
No, Gollum would not have been able to live in the midst of a community of Hobbits, had he been able to survive without the Ring. He is too ruined by the Ring, even if he could survive.
Gollum is no wraith. I don't see him shriveling like one. Maybe it would be more like Saruman, but something in this makes me think not. I think that he would return to being just a very, very old hobbit who, having nothing remaining for which to live, would weaken and die.
My two cents.
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