Honestly depends on my age. If it's before 30 or so, I'd go killing people, blowing shit up, other despicable acts. Got GTA Frenzy on everyone. Hey, fuck if i'm going down, everyone's going down. Mostly, plan shit out for the first 12 hours, and then do acts to people in secret, then the last few hours (as people start to discover shit) go total psycho.
If it's after 30 or so, then i'll probably donate my shit away, give some stuff up, complain about shit i couldn't do, and type up the general plot/summary/game ideas/whatever that i wasn't able to finish, so that other people can check and try to do it. write a will. play final fantasy or megaman legends 2 on hardcore mode.
Immortality but complete vulnerability to getting killed (not sickness or shit), or a invincibility/won't die or lose limbs for the remainder of your life?