Don't even need extenuating circumstances.
Docs "fire" patients all the time for not vaccinating their kids, not quitting smoking, being obese, no-showing for multiple appointments, etc. Not necessarily for these things themselves (aside from the no-show), but more because after countless conversations the "relationship" just isn't working out because the two parties aren't seeing eye-to-eye.
I have a personal acquaintance who is quite obese and this eventually led to chronic knee issues, including a couple of surgeries. Over and over again her doc emphasized that her weight was the source of the problems and until she lost significant poundage, everything he or the ortho specialists could do was merely a short-term solution. She didn't lose weight (just gained more) and kept hounding her physician over and over to "do something more". Eventually he just told her that he was sorry but he couldn't see her anymore until she had lost weight. Was quite sad since I saw all this from the "outside" as a friend of the patient.
The vaccine stuff happens a lot:
More Doctors 'Fire' Vaccine Refusers
Also, when you say you are familiar with "ethical laws", what are those? There are state and federal laws (legal system) and then there are ethical guidelines (set forth by specialty bodies and medical organizations). Not following one gets you fined/jailed while not obeying the other gets you dirty looks, bad publicity, and maybe in extreme cases a revoked license.
You are right about having to give patients adequate notice and time when "firing" them so that they can find care elsewhere if they so choose. Otherwise it may be abandonment.
It's interesting stuff. Obviously you'd hope that most doctors would only resort to such measures as a last resort, but it's important to know the distinction between guideline and actual law. I also think it's funny how the "abortion scenario" is a classic interview dilemma that almost everyone gets asked eventually... because that's not real life. PCPs almost never perform abortions, but rather the moms-to-be-(not) go to abortion clinics or someplace where there won't be any objecting providers to begin with.