If you fear that your dog has killed possum then it should be given rabies vaccines. It is better to take your dog to vet and get test for rabies. Mostly pet gets cured through these vaccines. The dogs can suffer from "Pseudorabies" that causes rabies. This is dangerous for your dog as this is an infectious disease.
It is better to call animal control department to get them out of your area so that your dog does not mess up with them
It is better to call animal control department to get them out of your area so that your dog does not mess up with them