Our Medicare program only covers health care in the US. If I decide to become an ex-pat and move to the South of France, I am not covered. Additionally, Medicare does not cover everything and one needs to purchase supplemental insurance to minimize costs. Medicare is also not free!!! There are deductibles and co-pays AND a monthly premium that is based on one's retirement earnings. The cost to my wife and I for our Medicare, pharmaceutical coverage, and supplemental insurance is about $15K/year ---- not exactly cheap.
Neither is the UK system free, insofar as it comes out of your national insurance payments which have to be made along with your state pension ones either through your employer making the deductions from your wages or, if self-employed, by you making regular payments. At the time when I was paying, the system was that you filled a booklet with little coupons/stamps every week and paid in that way. Also, depending on earnings, there used to be a percentage added to the annual insurance contributions bill based on whatever you were earning. Eventually, when I moved away, it was possible to pay a lump sum by cheque once a year. Much more convenient.
Where the concept of being free comes into being is at the point of delivery: you don't get flung out of hospital after treatment with a financial albatross of debt around your neck, nor are you refused treatment.
It was the reciprocity deal that allowed Bits to enjoy the same help in Eurpope as do the citizens of the host country, and of couse, the other way around. That's what seems likely to be sunk without trace.
If May's exit proposal deal had been accepted, Brits living abroad would still have been affected to a degree, with health aid restricted to the country of residence. In other words, as I live in Spain, were I wishing to drive to Britain, I would still be covered within Spain, but not when I crossed the border into France. As for Brits on holiday, I think they would have lost that former health goody too under May's deal.
No change was the better option for both expats as for holidaymakers.