Did I ruin my griddle by overheating it?
I'd say this one needs to be thrown out, or more fully disabled so someone else does not pick it out of the trash to use it and then thrown out.

The bubbly plastic bits in where the food goes are not a good thing, and there may well be some hidden damage as well.

If it was me, I would not replace it with the exact same model, either. I would expect the sides to be welded in place, or stamped into a solid sheet; not glued like that.