{SPOILERS}

I don't know what show viterbiSearcher was working on, but Valjean certainly does NOT die in the sewers. He collapses in the sewers long enough for Mr. Thenadier to steal Marius' ring, and then he gets back up and finishes carrying Marius away from the battle.

He dies later of some unmentioned old-age related sickeness shortly after the wedding of Marius and Cosette.