Some listing agents will stick buyers with closing fees that would normally be paid by the seller, let important deadlines pass without reminding the buyer, negotiate any inspection issues, appraisal issues etc. heavily in favor of the seller, check the specific performance box for the buyer in the contract etc., etc., etc.

That is rough but a good reminder that we need to have proper reserves. 

Maybe if we shared out down time in the fall, it will help remind us to do so.

This gives the remaining tenants another reminder of what will happen when someone leaves and avoids any surprises.

I would contact the Tenant and remind them that all adults must be screened and approved before they can occupy and that they must be added to the lease.

Hope this helps, I don't intend for it to sound too harsh but reading your post in the forum reminded me of where I was a few years ago. 

Remind them an eviction will follow them. 

I had to remind him he cannot demand more than 33% which he immediately agreed.

This reminds me of my steadfast refusal to add WIFI to one of my cabins. 

Now fast forward 5 months he cannot secure finacing.We recommend our prefered lender and lender asked him to submit his wifes docs which he never did.We have been reminding him 60 days ahead to secure financing and to get into a written contract with us.We send him a non renewal of lease letter 60 days prior .He took it lightly.Today i send him a notice to vacate and a cure or leave letter for extra dogs that i noticed in registered mail .He texted me saying he is really intrested in buying the house and open for our owner finance with low down payment as he donot gave any money.