I tested this tactic today against a fiery warlock. And i was surprised that it worked out very well. Although i must say the warlock made some choices that i would not have done.
I think you tactic works when the enemy is defensive or advances slow, but i would have been in a world of pain if he had rushed to my fortress of doom before it had finished building up.
Well yes, a Mage that rushes right at you is going to completely ruin this strategy. Although, when facing an ultra-aggressive build, you should probably realize that AoS is probably not the best strategy to use anyway
It takes far too long to build up when facing an aggro Mage. This is why it's important at the beginning of the game to make a snap-judgement about what strategy your opponent will use. Forcemaster will always be aggro, Warlock will be aggro/semi aggro, etc etc.
All the game i had a strange feeling. Although i controlled the game, i felt like a bird in a cage. The fortress can also be your grave without the chance of escaping if your enemy decides to burst you with ranged attacks from 2 zones away (or 1 zone, if you already got the cloak ready).
As long as your walls are up, they can't hit you with Ranged attacks because the walls blocks LoS. If your walls go down, I'd probably be more worried about the Teleport you also mentioned than a couple attack spells.
The defense seems to be pretty vulnerable to teleport-attacks. If your mage is teleported out of the fortress, hes pretty defenceless and your skeleton warriors will have lots of trouble to reach him in time to save his miserable life
Again, as long as the walls are up, you should be okay. If they get knocked down and you get teleported out, you can simply move or teleport your Mage back in and then QC another wall. You'll be getting hit for a few rounds while you move back in, but you probably won't die. While you're sitting behind the walls, you'll have a few free actions you can use to cast some armor in case this does end up happening.
If you see the enemy going up into that zone with the gas cloud to try to teleport you around the walls instead of knocking them down, you can counter this as well. You can throw on a Cloak of Shadows and just sit in your starting zone. That way they have to come down another zone to cast the teleport, which is not good for them, cause then they'll be in your little fortress with your Archer, Mort, your mage, and whoever else you have out there. & on top of that, if they have to come down to target you with the teleport, they won't be able to teleport you as far, making it easier for you to walk back into your fortress.
The killer to this strategy (as with most Necro strategies) is flying creatures, namely Adramelech. The reason is obvious, he'll just fly over your walls and start pounding on the Altar. If this happens, you'll need to have something guard the Altar. Mort might be best, that way he can counterstrike and hopefully get some Taints on the LoF. You want to make sure Mort doesn't die though.
You'll also want to carry around Maim Wings in your spellbook so you can help prevent this. Once he comes over the wall, you'll want to cast that on him and focus on killing him while still keeping your walls up. That can be tricky. If you have the Grey Wraith's you'll want to use those to attack the LoF to try to weaken him.
With Mort and 2 Acolytes in the same zone as the Altar, if you use both Acolytes to heal the Altar, you'll be healing it 6 points of damage per round. That should be enough to keep it alive while you're steadily damaging Adramelech and making him attack with less dice. Just make sure you don't forget to keep your walls alive.