Need help figuring out how to respond to move out date issue

[Tandi H.]

Hey, we could use some advice on how to proceed with a tenant issue.

• First, tenant let us know on July 31 that he would be closing on a house on August 31 and moving out by the end of Sept.  Based on his move-out date, we planned to use the unit at the beginning of October for an AirBnb that is booked starting Oct 4.
• On Sept 6, I asked him if he could move out a bit earlier than the end of Sept, and we would give him a rent refund for any early days.  This would give us more time to prepare the unit for re-renting.   
• In reply to my email, on Sept 6 he let us know that he hadn't closed yet, as he had switched lenders.  
• On Sept 10, he told me he would now be closing on Sept 24.  He did not say he needed to change his move out date.
• On Sept 10 I replied saying that he could continue to use the garage to store his stuff into October if that would help him with his transition.  We just need the apartment portion of the unit.
• On Sept 13, he let me know things were pretty tight to move out at the end of the month, but did not request a date change.
• On Sept 16, I told him (nicely but firmly) that we were counting on his end of Sept move out, and that we needed the unit Oct 1st.  
• Today Sept 18, he told me that he wasn't able to be out by end of Sept.  Here is his full message:  

"Given the multiple changes and delays with my mortgage, being out by October 1st is not realistic. Per my email on September 10, the revised closing date of September 24th is my written 30 day notice. I apologize for any inconvenience this may cause. It just makes me extremely nervous to agree to a move out date of October 1st. If any other delays occur I would not have a place to live, so I can’t agree to that. I want to give you as much notice as possible that I will not be out of the apartment by October 1st so you can make any necessary arrangements. As soon as I have firm move out date I will let you know. However, the move out date will definitely be before October 10th, which is the expiration date of my written 30-day notice. If you have any questions or concerns, please do not hesitate to contact me."

What can I do?  Do I have any options?  It doesn't seem like any legal action makes sense given the timeline, and also he's been a good tenant until this.  How should I handle his Oct rent?   This unit rents for $675/mo, and his deposit is $650.  What about telling him he can use the garage into October - should I revoke that or make changes to the offer?  How much do I charge him?  

Thanks in advance.