This is one area where the usual rules applying to whether expenses are covered by Medigap plans (ie that you're not covered unless covered by Medicare) don't apply.
I called Mutual of Omaha before our recent trip to Europe, and was told that over the phone that yes, basically they would cover 80%, and if necessary I would be transported to the place of their choosing, which might not be back to the US (eg, to Germany from Switzerland). BCBS said the same thing for another traveler. I don't know whether/how this differs for pre-existing conditions, but that wasn't mentioned as a factor by my agent. Since expenses are so much lower outside the US, additional insurance seemed unneccessary.
This is standard and required by our government - from
https://www.medicare.gov/supplement-other-insurance/medigap-and-travel/medigap-and-travel.html :
Medigap coverage outside the U.S.
If you have Medigap Plan C, D, E, F, G, H, I, J, M or N, your plan:
- Covers foreign travel emergency care if it begins during the first 60 days of your trip, and if Medicare doesn't otherwise cover the care.
- Pays 80% of the billed charges for certain Health care services or supplies needed to diagnose or treat an illness, injury, condition, disease, or its symptoms and that meet accepted standards of medicine.
Foreign travel emergency coverage with Medigap policies has a lifetime limit of $50,000.
Find out before you go
Before you travel outside the U.S., talk with your Medigap plan or insurance agent to get more information about your Medigap coverage while traveling.