Eh - shorter than cancer, and Heisenberg ends his life on Heisenberg’s terms. His ego won’t let him waste away to nothing, not after all he’s done and gone through to create this brilliant catastrophe.
There’s always the Scarface option - which hints towards the M-60 and the scene where he’s watching that movie with Walt Jr.
As soon as Walt said “oh man everybody dies in this one” watching scarface, I knew how the ending was going to go.