|Can you replace the case???? Yes and no.|
Some dells have the mother board on a tray. Board can be replaced in under ten minutes. But trying to put that board in a a different case is a nightmare as the wiring to the front bezel has to be reworked. ....and the front usb. Then there is making clips to hold the tray in the new case.
Even if not on a tray....your in for a time.
If the case is a wreck ...you can usually find a good
(same model) case on ebay that is empty for just a few bucks.