The base of the island is probably installed with pocket screws. When the slide hit the trash can and the can pressed up against the island, the screws pulled out of the floor (my guess)???
If you can see the actual wall of the cabinet that touches the floor (from the inside), you'll probably find the screws. The screw holes in the floor will probably be all busted out. You'll need to remove the old screws, otherwise, they'll continue to try to poke back into the floor, and they can't. They have to be screwed in. Remove the screws, then glue up the floor where the screw hole is now torn up, and you might be able to rescrew it back down.
But the reason the cabinet is not going back flat is because the screws holding it to the floor have been pulled out.
One more thing. Those screws will probably not be a Philips headed screw. They most likely will have the head that takes the square headed driver end.
