WMG: Beetleborgs

Beetleborgs Metallix ends without resolution because the monsters finally ate the kids.

Once the Beetleborgs no longer existed, the door to the 2-D universe was sealed, meaning the Crustaceans could no longer sustain their existence.

Alternatively, the series' resolution happened offscreen...

...And it was with Zordon's energy wave destroying the Crustaceans and taking away the Beetleborgs' powers once and for all.