I know that stale blocks usually happen by accidents and the chain that has more blocks will be chosen as canonical chain by default and the stale chain is discarded.
My question is about what it means to be discarded?
Is it permanently discarded?
Or does it mean that if those stale blocks become longer (from 51% hash rate mining), they will stop being stale and be preferred by nodes?
I simply want to know whether it's possible to alternate mining between 2 chains making them roughly equal in length when you have 51% hash rate so that the network becomes useless. I think that it doesn't make sense that stale blocks are completely discarded. Because that means the longest-chain rule is not obeyed. If you obey longest-chain rule, stale blocks must always have a chance to become part of the canonical chain no matter what.