I'm sure I don't speak for everyone, but I'm sure I speak for many saying if my world(s) were folded, I'd leave HBD. At least for a while. And I'd think hard before I came back, because I'd figure WIS would probably do it again.
I like my worlds. But I like my teams more. I wouldn't like it if one of my worlds folded, but I'd go on if my team moved into an existing world. Ideally they'd let me pick among worlds that agreed to take in teams.
History would be screwed up, but that's a lesser issue than taking teams away from people who invested 1-2 years, a lot of hours, and $100+ in to them. So what if I look at a player card and it shows he was MVP two times in another world? I'd rather that than wipe that players history. NBA history survived taking in the ABA. NFL history survived taking in the AFL. WIS could figure out a way to bring in teams and keep player history.
If you've never played HBD and somehow you landed on the HBD Join A World page and you see 100+ openings, you're going to think the game is no good. If you walk into a restaurant that could seat 100 you've never been to on Sat night at 8 and there are just 6 people in there, you''re probably going to turn around. Same effect in HBD. Moving teams into existing worlds would solve a lot of problems.