RE: Backup plans....the good thing is that the majority of ex-full-timers don't want to go back to the way they lived.
They will want a much, much smaller place to buy and probably in an altogether different state to live. A park model in a permanent park would suit them just fine. They are used to living in small spaces and not 'collecting stuff' once again. They are also used to being someone warmer in winter and cooler in summer. They're attitude about just about everything will have changed. Exit plans don't always work. Full-timers are used to being flexible. You really can live much more cheaply than before full-timing.
Many medical issues can be dealt with just fine in an RV, park trailer or mobile home. In fact, from experience it's really much easier to recoup because the space is smaller with less walking. A ramp or lift can be used for entering and home health care will come into the RV to help out. We've dealt with surgeries, joint replacements and cancer. All is easily doable.