I read a while back on a supposed screenplay for a spinoff Boba movie. Basically that kid in ep3 is Boba, but a better bounty hunter comes around and takes his identity. That being said, even IF the rotj boba died in the sarlacc, then perhaps someone harvested the remains and became Boba.
While we never see anything in the official canon on Boba even being good, the only thing that really is prevalent is his reputation. So anyone with the armor could potentially inherit that reputation, making the armor valuable for a scavenger.
Hell, that's even a plausible way for him to escape. Scavengers come around a week later hoping to remove the armor and dead Boba from the Sarlacc only to find Boba still alive in it. Boom, Boba lives.