Guys why trying to remove my rear brake cover one of the bolts after having unscrewed it a few mms just started to turn around in the rivet.

ie the rivet is in place but bolt just turns around and i cannot take it out - now questions

1. once i cut the head off - i cam assume i can fish the remaining bit out through the DI 2 battery hole right?

2. any idea how to replace this rivet? with thread

3. any other ways of getting the cover to stay in place?

appreciate helps