From what I understand based on what a WC lawyer told me two years ago, the WC pilicy that was held by the company you worked for when you were injured, is the WC policy that is responsible for paying all medical cost related to that injury. It does not matter if the company you worked for no longer holds that WC policy, you move, the company you worked for goes out of business, etc. It can become more difficult fighting for coverage under some situations, but unless they made some sort of lump sum settlement, they are required to pay all medical expenses needed over your lifetime that are related to the original injury. That includes PT, or any other rehabilitation that provide any gains or relief.

That is how it is in Michigan. Every state has different WC rules though. You could always talk to a lawyer to get a better understanding of the rules in your state. Just talking to a lawyer over the phone usually does not cost anything unless you sign an agreement or pay a retainer.