I'm kind of surpised that the hypothetical proposed has generated such extensive conversation.
I suppose everybody plays rpg's for different reasons, so perhaps for some folks, the thought of permanantly slipping into a medieval fantasy world -- however midguided -- is appealing.
Me? I'll pass. My reasons have nothing to do with the nuances of age, culture or survivability, but you're right that it wouldn't be a game anymore.
I play rpg's as an outlet for creativity, and the fun of being someone else as much as being somewhere else. Although I enjoy that bit of escapism, I'm pretty happy with who I am in the real world and wouldn't swap my life for anybody's anywhere. Seriously.
As for being somewhere else... I haven't begun to tap into all the adventures there are to be had in this world. And I seriously doubt that anybody who said 'yes' to this hypothetical invite did so because they've exhausted all of earth's excitement.
Perhaps I might feel differently if my life was subject to different circumstances (age, disease, etc), but I can only base my decision on what I've got.
RPGs are fun, but, for me, so is having real-life adventures, and I'm pretty happy with the campaign setting I'm in.
Thus endeth my Dr. Phil self-esteem sermon for the day....
zog
PS: Besides, in the Forgotten Realms, nobody plays Spycraft or Alternity or Skull & Bones or Shadowrun or .....