Here my not so different suggestion and Cirn0 takes on it.
http://fonline-aop.net/forum/index.php?topic=2417.0My takes on it is that if that guy hides well, he can hold the contest as long as he stays alive, to protect the zone or wait for reinforcement. It seems totally ok to me that he holds the contest as long as he is still alive.
On the other hand, he shouldn't hold them longer than the time it need to get him. If he comes at the very first minute and it takes you 11 minutes to get him, you should have the zone right after he dies, not having to wait 9 more minutes.
It seems to me a better balance between the right to defend its zones even alone, and the right to the attacker to take the zone if they got rid of the guy, without having to wait more.