Is There a Way That Enamel Lost from Interproximal Reduction (IPR) Can Be Regrown?

The reason dentists place fillings is because enamel cannot grow back.  It is likely that IPR was necessary for your case to work, as this is a very common process in orthodontics.  Usually, the amount is so minor that you should not worry.

Be sure to not be quick to judge treatment in the middle of the process.  Often, things get worse before they get better.  If you go back to orthodontics, trust in the dentist or orthodontist and let things happen.  Feel free to ask questions, but be prepared for things to look worse at some point.

If the spaces bother you you might qualify for a retainer that can close those spaces or you could restart your case with a smaller fee from another orthodontist...

The IPR shouldn't cause any long term problems. Didn't the orthodontist who delivered the case have the rest of the trays that he could give you or transfer to another dentist? Usually IPR isn't done until the case is ready to deliver. That would be ideal if you could get a hold of the dentist and see if a transfer can be done.

Also even when there is a bankruptcy, the practitioner is still obligated to finish treatment that has begun per his/her state dental license. If they don't finish treatment they should be accomodating to help you find another dentist. There are patient abandonment laws that prevent a practitioner from abandoning a patient who is being treated by him even if he is no longer financially responsible for the treatment anymore. Good Luck.