Yes you do lose seniority if you're afk, but did you try to contact him mic/chat before changing maps?
I'm not sure why I should have to if the AFK Manager has provided absolute, incontrovertible proof that he has been idle for a period of 5 minutes, which is the amount of time an admin can go idle before losing seniority.
*DEAD* [SF]Rios( . Y . ) : my god u are the monster not the zombies
*DEAD* [SF]Rios( . Y . ) : lol fu u
~ said shortly after being stuck in a cade and killed