Just a stupid theory.

I believe two things may happen.

If any of the residents of Fromville are able to leave by the end of season 5 and break the cycle.

1. The night monsters may permanently return to human form and be forced to leave too. The bus is still usable (after a puncture repair) and that could be used to get them all out at once.

2. The residents return to a point before they arrived and continue on with their lives with no knowledge of what they have been through.

Possibly the big bad survives to play another day.