I think the chances of bandai actually snatching DBO back are really low. Considering how big DBO was when the servers we're shutdown 3-4 years ago, don't you think the fact that it was being brought back by some german guy would've eventually reached bandai's ears? To be honest I think they really don't care and are fully aware of DBO's revival considering how big a hit Xenoverse was and the fact that they'll most likely be cashing in on the upcoming sequel. If bandai really cared they would've shut things down while we we're still in alpha.
Nostalrius was a vanilla World of Warcraft server that was IMMENSELY popular. It went on for years. Then, last year, Blizzard finally shut them down.
Just because your project isn't immediately shut down doesn't mean that you're out of the clear. It's woefully optimistic to assume that they don't care about DBO anymore because they have a new game. Bandai is still a business and I doubt any good business would willingly let someone else use their product for free, regardless of if it's still a supported product or not, and let that person make money off of it.