It is very possible that the Amhole can completely seal up, despite the lies troons tell themselves. I'm not a wound expert by any means, but I'm sure you're familiar with the process of a scab healing. That is what the Amhole is doing constantly. This is why troons have to dilate, the body sees the Amhole as a wound that needs to be healed and the ways that can happen is 1.) a troon continues with dilating for the rest of his life, creating scar tissue that will serve as the "vaginal lining". 2.) a troon gives up with the maintenance of the Amhole, which causes it to close in on itself and still create scar tissue which will prohibit access to the "vaginal canal".
There are different ways in which surgeons conduct Amhole surgery, and the is no one "true" way to perform MTF SRS. This causes complications as since it's an experimental surgery, class action lawsuits can't really happen as there are so many different types of procedures.
As for how he will pee, it's difficult to come to a conclusion. I believe that during penile inversion surgery they makeshift a urethra separate from the "vagina", so there's a chance that Kevin would still be able to pee with a zero-depth vagina. I'm not aware of any troons who have had surgery where the Amhole and the peehole are in the same hole, but I'm sure its been done somewhere in the SRS disasters thread.