i’d say no, because dementors aren’t necessarily alive, yk? and i’m pretty sure a patronus is the only thing that can fend off a dementor, because if the killing curse worked i’d assume students/teachers would use it on them since they aren’t human so it’s not illegal

It probably doesn't but it's been said to be really hard to cast.

Probably not, seeing as they're not technically alive

Dementors are "amortal," meaning they're not truly alive and therefore can't be killed.