The one with documentation wins.

You could take legal action against the buyer to force them to follow through with the deal, but you probably wouldn't win.

Has anyone had experience with this and/or have any ideas on how to create a win-win situation?

  ( I dont think you would win due to the destruction )I dont think you will have a problem finding another tenant , peoples homes , businesses and cars were washed away , they are sleeping in shelters  . 

I want to propose an owner finance deal but I need ideas for a win/win structure.

That's a win in my opinion and many others.

In addition to looking at their reviews, see who wins the SEO war if there are multiple PMs with direct booking sites.Google the lake name + cabin or rental house and see who pops to the top.One other question I like is "What makes you different?"

The professional tenants are everywhere and in CT, they'll win.

I’ve actually done deals with & been business partners in commercial deals & hes bought a couple properties from me as an agent thus far so trying to figure out the best way forward to make it win win for for everyone 

If you were able to find a place that allowed you cover at least a sizable chunk of the monthly expenses, and keep your monthly outlay at or around your current position I'd say that's a win.