Originally Posted by
Tendrin
It's more complicated than that with varying portrayals between writers, of course. Remender has Bob declare that the Void had gotten bored of coming back to life and dying with him over and over by leaving for the 'white hot room'. It is not, however, like Bob was exactly sane at the time, both due to the death seed and the impact of burning to death in the sun willingly over and over in an attempt to stay dead.
The original mini implied that the Void had broken free of him to become more of a separate entity but it's also implied in other works that it's very existence is a delusion created by Bob's vast powers. And Bendis, of course, famously implied it was the angel of death quite inexplicably.
Yeah, it did possess Doc Strange during the Loki arc.
It's complicated and confused and I barely scratched the surface on some of the confusion around it over the years. Hopefully, Lemire can sort a lot of it out. The most important point is that there is a reason the Void stops existing if Bob forgets he's the Sentry.
As for vulnerabilities, yeah, some characters do have powers that turn off and on. Bob's Cary a lot by mental state, of course.