Ancient heroes entrance is ment to make trouble for pking ppl so I wouldn't change this .
Letting ppl going in once only would make some get probably all the drops because other ppl wouldn't be able to go for a 2nd time. It's already almost impossible for people outside CHN/bs to get any drop so don't make it even harde for them.
If you are getting attacked at entrance you would need to buff and kill them to not die. I think this is just helping the guy thats getting pk'd unless you die to the pker
Also if people would get locked out after a death it would make it easier for small number players to win the fights. You would only need to kill them all once and your team would own ancient untill next reset.
Right now if you kill a player in ancient they are back in 10-15 seconds with no penalty. There is no party buffs so they just need to buff themself again. You can get back instantly 3 times atleast, more if multiple ppl are willing to summon you.