I had a tummy tuck in a private hospital a few years back.
I asked my surgeon (who retired from NHS plastics a couple of years before my surgery) what would happen if I had complications. He explained that my price included 6 months of aftercare so if I required an extended overnight stay then this would be covered and I would remain in the private hospital.
The hospital had an ICU department which could deal with most issues but if not then I would be transferred to an NHS hospital for life saving treatment and then back to the private hospital once stable until ready for home.
I asked how many of his patients in the last 3 years had been transferred to an NHS hospital. His answer was zero of about 1000 patients.
However, he was quite strict. He would only undertake such invasive surgery if I was not overweight, agreed not to smoke or use nicotine (didn't apply to me) for 4 weeks pre and post op. Would not consume alcohol 2 weeks pre op and 2 weeks post op. I had to stop my contraception 4 weeks before surgery and have a separate consultation with the anaesthetic team 1 week before surgery.
He wrote to my GP asking of they had any concerns about the planned surgery.
I had reviews scheduled 7 days, 2 weeks, 4 weeks and 3 and 6 months post op. I had open access to the surgical ward and I was seen to have a seroma drained.
From reading posts on social media from people who went abroad there were no such checks and they would operate on anyone. Also they couldn't understand that a seroma is not a life threatening issue so the NHS will not drain it. It looks awful but will resolve after a few weeks in most cases. You can purchase specific plastic surgery insurance. If they decline on pre existing conditions then it's probably a sign that the patient should not be having elective surgery.
The aftercare is the most important part of the surgery according to my surgeon.