What are the possible fates of a blue supergiant?

Answer 1

A blue supergiant in most cases will explode as a supernova leaving behind either a neutron star or black hole - depending on the original mass.

In very rare cases, it could form a oxygen-neon white dwarf.

Answer 2

Possible fates for a blue supergiant include eventually exploding into a supernova, then collapsing into either a neutron star or a black hole depending on its mass. Alternatively, it could shed its outer layers to form a planetary nebula, leaving behind a white dwarf.

Answer 3

When the star dies, the energy created in fusion is insufficient to hold the star "up" against its own gravity, and, having exhausted its "regular" fuel, it will collapse.

This is the supernova process.

The star collapses, causing the outer layers to violently explode outward as gases and dust. The compression of the body of the star in the collapse creates enormous thermal energy that supports the endothermic fusion reactions that create those trans-iron elements (up through uranium).

It all occurs in a relatively short period of time. Afterwards, the remnant core may become a super-compressed neutron star, or even a black hole, if the star is massive enough.