The cannister being plugged would not cause the tank to collapse. It would prevent the suction from getting to the tank. The Fuel Tank Vent Valve is (or was) probably the culprit.

Back to your original question. If you can live with 9 gallon capacity, you can leave it as is. I wouldn't myself because I do a lot of distance driving and need larger capacity. I would remove the tank, purge it and see if I can pressurize it and pop it back into it's original shape. Be sure to leak check it afterwards to make sure it didn't develop a crack somewhere. Don't do any of this until you get all the gas fumes out.

Wes