Root Canals, and the time one was done on the wrong tooth

I never had a root canal until this month, and I surprisingly came out with 2 today! I know nothing about what to expect down the line with these things, and was hoping I could get a feel of what other people might do in this situation. Here's my totally awesome story:

I had throbbing pain, and went to a new dentist who agreed to take me in that evening. The guy did x-rays and showed me the abscessed tooth, and I heard the dreaded words: Root canal. My very first one. He explained everything to me and everyone was great. He did a partial (it was late) and put temporary filling in, and told me to come back in a few weeks to get a permanent filling and a crown.

Fast forward to today. He finishes the RC, looks at me, and says, "I have some very embarrassing news. I did the root canal on the wrong tooth" ... and had to sit through him doing the RC on the right tooth. This wasn't a case of misjudging the tooth that was in pain, he was just plain neglectful in making sure he drilled BACK into a tooth he already drilled into once before. Not to mention the wrong tooth was perfectly fine.

He didn't charge for the wrong tooth, but he also said it didn't need a crown. With it being a molar, is that true? Why does the other tooth need a crown but the other does not?

I'm not sure what to expect in future cost of this tooth now, and what I really should be asking of this man or the practice he works for. He's older and am not really sure how much longer he has to practice. If I need a crown, or a replacement crown, or an extraction and implant, how do I assure that I don't get stuck with the bill down the road?
I get mistakes and have no interest in suing or ruing whats left of this guy's career, but I also don't want to be screwed later.

Thanks everyone in advance for any responses!

I would get this mistake in writing. Is it in your journal? Could you get something signed? Maybe even a written promise of free care for that tooth?

Yes it is in my record. I think I will talk to the manager of the practice next week and see what can be done.

I got 3 root canals 2 years ago, just keep your teeth clean and it should be fine...

But if he took the root out of that tooth, it most definitely needs a crown. Teeth without a root will become brittle and break. If he didn't drill down to the root, then a simply filling should be fine as long as it's done correctly(I have a crummy filling from a dentist I hated and there's holes between it and my tooth that I can feel, I have to go in and get it checked out)