It depends on what the remote server does with the federated delete command. You should generally assume that anything you post to the fediverse is permanent.

This is only from what I have seen and I have no knowledge of how federation works:

No. Ex: there have been many spam posts on [email protected] that I made a post about. I found out from that post that they were removed from the kbin mod, but I could still see them here on Midwest.social.

See this post for more info. There is also a link in there about this known issue.