Keep reward vault open post event

bazalenko

It would be great if for events like Unstable iso-8 where the rewards are from their own vault that this vault would remain open for some time after the event. This would allow people in the last slice to use their tokens (and those from alliance) in the vault before it becomes post-event.
This would have allowed me a 4 out of ~70 chance for 4* rather than the already reset post event one which is 4 out of 80