As long as you did not kill Laiken, you can go back to the cave of the Necromancer in Brocen Valley!
You didn't find the Necromancer? A locked door? Maybe you must finda key somewhere in that cave! I didn't remeber a locked door, but it is for sure possible because you must go through 1 gate and 2 doors to come by the Necromancer, "Naberius" is his name.
The first gate on higher region nearby the Chapel Waypoint Scrine and a Goblin camp ...is so far I canremeber 'not locked'.
The two 'doors' you must pass after go in the cave via gate are closed, but or they locked too?
The first 'door' I think is locked, but a key you can find nearby this door .. and the second 'door' is not locked if I remeber right.
Beware of skeleton warriors behind the first door! But I think they do you nothing more if you are already in the Maxos Temple, I think you 're at laest a level 12 - 15 hero(in) !
Take the Crypt Waypoint Schrine inside the Maxos Temple to the Chapel Schrine and give it a try
If you can't find Naberius, I'm afraid you have a bug
(but can't remember someone report ever a bug like this ... )
Success!