I too have had the pleasure (?) of being the Dr. on board, and until my last call up, had always answered the crew request. However, last one (now several years ago) was to attend the Captain, who was feeling dizzy, on a transatlantic flight ex-LHR and advice was needed prior to reaching point of no return to LHR.
To provide confidentiality to those involved and to cut a long story short, yes a medical issue which was ongoing, but no not something we needed to turn back for, and yes, very polite grateful CSD and flight crew including the 2 x 1st officers who took over, no not a single F/U from BAEC or the airline, despite my GC status. To be fair, I was not expecting anything as getting safely there (and on time) was recompense enough. However, what has stopped me from answering the calls since, was advice from my medical practice insurers of the risk of medical malpractice lawsuits, especially for flights to and from USA…. It seems it is just not worth the risk.
Of course, you will have a duty of care morally, and in some countries (France, so presume French airspace or French carriers?) a legal duty of care as well to respond. Have been lucky never to have had to test that dilemma as another medic has always piped up early!