Contact the Probate Registrar in your Area and inquire if your parents' wills have been filed there. If the original is on file, it doesn't matter if the copy is destroyed. If the original is in your parents' home and has not been filed, then you need to take steps to preserve the will.
Has the testator died?
If not, speak directly to them and ask them to register the will or send a copy to a trusted 3rd party. Also the attorney who drafted the will may have a copy and any executor may have a copy.