This scenario seems unbalanced in favor of the dwarves, even playing with the variant that the necromancer gets another baleful gaze token every time a dwarf dies. This is the first scenario that that variant couldn't acceptably balance.
The trick for the dwarves is to move fast, before the pits of souls can churn out enough skeletons. That means foregoing the son of stone ability, you will need the extra movement. But on the first turn, just move far enough to get a good position for a dash for the exits.
On your first turn, start by having the second dwarf from the left move up the hallway and engage the skeleton hound. That's an auto-kill. If he kills the skeleton hound, then the dwarf on the far left moves into the room above him with the pit of souls, stopping just inside the room and diagonally adjacent to the pit of souls.
Then the dwarf that just killed the skeleton hound uses a follow-on action to advance into the same room as the far left dwarf. He also stops just inside the room, but orthogonally adjacent to both the pit of souls and the far left dwarf. With a dwarf token pool of 4 IIRC, you should have a follow-on action to do that.
Now both dwarves are side by side, adjacent to the leftmost pit of souls. If the revenant in that room moves to attack a dwarf, then he is attacking outnumbered 2 dice vs 4 so good luck. Summoning a skeleton from the pit of souls means two free strikes on that skeleton, 4 dice vs 2 with 1 armor. That summoned skeleton is either boned or dusted, so you've locked down one pit of souls. No skeleton other than the revenant can reach those two dwarves this turn, absent a baleful gaze.
Baleful gaze netting you another attack with the revenant at 2 dice vs. 4 is likely a loser and then the dwarves will massacre the revenant on their turn 2 with outnumbering. Your other option for baleful gaze is to move a skeleton partway over from the next room to the right with its full action, then use baleful gaze to give that skeleton another full action to close the gap. That skeleton moves on top of the pit of souls and attacks with his full action. It is still 2 dice vs 4, but now you have two skeletons clogging the dwarven path forward on turn 2.
Likely though the dwarves will be able to blow through the revenant and skeleton on turn 2 and then race for that far left exit. Game over in 3 turns.
What do you do with your other regular actions on turn 1? Well I think you might use one to advance the throwing mastiff to protect the flank of the dwarves on the left and maybe tie up a bone pile, don't recall with the mastiff. But the dwarf on the far right should advance along the far right wall, as far as he can but staying just out of reach of the revenant in the room above. Now you are threatening the right side too. If that revenant doesn't burn a baleful gaze to attack the far right dwarf, then if you get 2 free actions on turn 2 you can actually run this dwarf around the revenant using the tunnels and avoiding the other skeleton hound. That's victory too.
We played this scenario a number of times and the above strategy seemed optimal for the dwarves. It consistently produced a dwarf victory. The necromancer can't respond fast enough to effectively block the dwarven rush on the left. For balancing, the necromancer probably needs a few more skeletons scattered around.
We tried son of stone too, it is more of a cat and mouse thing but basically it also gives the necromancer time to consolidate forces. There may well be winning strategies with son of stone, we just found the basic dwarf rush to be ample.