Ok, I did a test and I found out that the dedicated minigame button works almost fine.
When a non-admin player builds something, and leaves all of his item spawns will still work except for grenade spawns, and possibly some more.
Anyway, when I, the super admin built and left, all item spawns seemed to work normally.
I'm also I little sad about not being able to change the mini-game color from green, but that's just minor.
Conclusion:
I can leave the game, if I take over ownership of bricks with destroy -> load without brick ownership beforehand.
If I do not do this, the grenade spawns will stop working after the builder leaves (given I'm using Default Minigame). I'm not sure if this is only in v9, but I doubt it a little.
I could really use a quick fix to this problem, so grenade spawns would work normally even when the non-admin player who built it leaves the game.