@Renee-And-Miguel0 Hmm, this is a tricky situation.
From what you describe it sounds like he was in such medical distress being admitted to the hospital that he left his cell phone rendering him incapable of contacting you. It sounds like an unavoidable circumstance.
Whenever I've been unable to contact a guest or they have been unresponsive I contacted Airbnb for assistance. They have more information such as emergency contact info.
I'm curious to know your rationale for changing the locks.
Not having any more information, my guess is that Airbnb would side with the guest and decline to charge the guest for the cost of changing the locks.
Clare