Perhaps the sarlacc can keep him alive. Like Spider's do when they paralyze their prey and wrap them up. Whether the Sarlacc can keep Fett alive for 1000 years, I dunno, sounds more like a local legend than actual fact, meant to scare the kids and stuff, but I'm sure Fett would suffer a great deal before finally dying.
this isn't really related, but as we were talking about Boba Fett, I read in the latest SW Insider that Temeura Morrison (jango Fett) was involved in the latest round of reshoots for Episode 3, not sure in which capacity, possibly as clone soldiers I guess .