I don’t know the specifics of what may have happened with Lemmy.film, so we’ll have to see if someone else may know.

As to what happens to posts to “their” communities, my rough understanding is that with the host server gone, federation either doesn’t occur or maybe attempts to reach the host but simply stops after some number of attempts. Upon failure I think it simply collects the posts on your home server/instance’s copy of the community.

Not sure what would happen if a new instance was spun up of Lemmy.film either from a backup or in general, but I’d imagine there’s some settings/adjustments that may be calibrated to prevent it getting a backlog of posts dumped on it causing it to get bogged down or crash.

As to questions specifically about the Lemmy software, you may try !lemmy_support@lemmy.ml or !lemmy@lemmy.ml, think either one would be okay for this.