The solar company I bought from has filed chapter 7. If they aren't purchased, what happens with the loan? Am I still responsible?

The solar co will send you a notice of whoever picks up the servicing/rights on your loan. As long as you pay them, you are fine and no negatives on your credit, you just honor the deal you made. When rights under a loan change, there is a grace period but do the best you can to be on time   good luck