If I message a client after they have cancelled a booking, will they still receive it?

I had a potential client come to my home today with his dog for a Meet & Greet. Everything was very last minute and I had just finished sending another client's dog home, so I really wasn't prepared for another guest. He needed someone to sit his dog today; all last minute stuff due to his previous sitter cancelling on him. Unfortunately, the dog wasn't a good fit for my cat. My cat got very stressed out and attacked me during the meeting due to the dog aggressively chasing him around my living room. I wanted to formally apologize for any inconveniences to the client, but I am uncertain that he will receive the message. So if I message my client now, after the booking cancellation went through, will he still receive it?