For "normal healthy" folks the odds of something catastrophic, travel-prohibitive, occuring are very slim.
Heart Attack - ok, you'd get emergency care and stabilized, but probably have to just be driven home or get amtrak across country - but that's an outlier for someone with no heart disease who is getting regular check ups.
Wife found a lump? go home, but not in a rush (work out a change on your return flight for a fee). Even after testing it's a few days at best to get a result, and doesn't always even mean immediate surgery. First step would be call and talk to your primary/gyno.
Accident/break a leg: Emergency care, then go home if you can't do the rest of your trip in a cast, etc.
Beyond that sort of thing, no you can't insure for every scenario. You could stay home in a bubble but then what was the point of retiring. But yes if someone travels extensively and frequently, and has the option to get a provider with some sort of national coverage (like Blue) then it's worth the effort.