The author of the fork declares 100 percent compatibility with the original project's database. As you move, the database structure will be changed (new fields will be added) to be compatible with the fork, but it will still also be compatible with the original project (which simply will not use these new fields).
I used conduwuit for a long time and it seemed very stable. Now I don't host my server anymore because my friend hosts his own server and lets me use it, so I have an account on his server.