do you have health insurance in your home country? If you do, most insurers will pay for overseas emergency claims. Some will even pay for planned* treatments - but you'll have to read your clauses very thoroughly. You are advised to buy something cheap in Thailand to cover the unexpected and unforeseen health issues.
Alternatively, you can also decide if you'd wanna buy health insurance in Thailand to replace the one in your home country but you'll have to jump through hoops if you have existing medical conditions.
Hope this helps. Nothing is easy but it's kinda fun exploring and manoeuvering through all the possibilities.
1. Why does your friend think he can shit on Thailand and do whatever he likes? Did he not know they have prisons there?
2. If his passport was all stamped out, why didn't he get a new one before flying into ANY country?
3. He flew in with his father whom I presume is in his late 40s to 60s. I'm assuming his father is still of sound mind. Why didn't his father help to oversee this matter? Isn't this what fathers do for their children?
Sorry if I sound negative or chiding but this is not an unforeseeable problem. Sounds more like an attitude problem where your 19 yo friend thought he can do whatever he likes in countries like Thailand. I do hope things go well for him in the end but please advise him not to do things like this again. Also there's no guarantee that he can come back again so fast with his new passport. Thailand would record that he overstayed and may blacklist him for a period. It would be prudent for him to check with immigration before he leaves. All the best to your friend.