I have read and understood the case play, but don't you think it changes when it is the 5th foul versus 2nd or 3rd? In the case play the player is leaving the court before their legal substitution opportunity. In the OP's case of a 5th foul, the player is replaced immediately anyway, so I think they are leaving during a legal substitution opportunity. Unless the interpretation is they can't sub until we inform the coach and start the timer...

What do you think JAR?