Could I have assigned it to a different buyer once the original buyer had broke the terms of our agreement? 

Do you hold any tax liens that you can foreclose the houses without dealing with the seller you can't contact?

The reality that neither view is realistic or probable.The best advice I can give would be to underwrite for long-term leases as that can be an acceptable exit strategy, but be prepared to execute well on your MTR strategy (great interior design along with profesisonal photos and concierge servive). 

Then if you want to pick up a first time investor buyer and show them the ropes of the most successful long term investors in your market you can share your time and expertise now and then.

Our market is very heavy tourists, so a lot of individually owned STR condos, but honestly I've personally have had more success in long-term rentals doing the BRRRR strategy with small multi-families and B-Class SFR's. 

I've crafted terms that are a win for me and for my buyer, but my intention is to hold the deed of the property until the buyers's note to me is paid in full, exactly as the banks do.   

We go back and forth between long and short term rentals.

Now is the time as my wife and I have further discussed short term rentals and such recently.

I would suggest you use your VA Guarantee (VA Loan for short) to purchase a home.

Those sounds like good terms.