Yes, you can get a replacement plate amplifier to fill the spot of the old one. However:
1) You'll have to make sure that the new plate amp will fit properly into the old opening so that there are no air gaps.
2) You'll also have to evaluate if it's worth it or not. If the original sub was only a $100 sub and the replacement plate amp is $120, then it might not be worth the effort.
But, let us know which subwoofer you have. From there, some additional suggestions could be made.
everything is repairable, but sometimes the cost of repair excedes the value of the item, how is the driver? surround in good shape, if it's marginal I wouldn't bother with the amp (did the amp also take out the driver when it died)