yes he is dead. here's a bio of the last part of his life
The assembled heroes' allies, the team X-Factor, sought out the cause of the strange disturbances and were easily defeated by Proteus/Piecemeal. They were sent to a place where the other heroes and residents of Muir Island were being kept. Jean Grey (now, Phoenix), at the time unable to use telepathy, used telepathy of the mutant Legion to communicate with Proteus/Piecemeal. The merged being decided that it would never be happy in the world in its current state, and the world would never be happy in the one that they sought to create. So they committed suicide by dispersing their energy form once more.