A lot of the suppositions are done with impossible to happen stuff, like the sun literally disappearing, or collapsing into a blackhole with no added mass (a sun mass blackhole would be stable, but I don't know how one could be created).

If it disappeared, then we'd still feel even gravity for those 8 mins, as the effect of gravity propagated at the speed of light. If it somehow magically became a black hole, we'd still orbit it the same even after 8 mins, but losing all the head would eventually kill us.

The expected explosion wouldn't be what makes the earth uninhabitable either. The sun increases in luminosity by ~1% every 100 million years, and it's estimated that between 700 million and 1.5 billion years the surface of the planet will be too hot for liquid water. An astronomer also says photosynthesis would be impossible in 500-600 million years.