I'm glad to hear it seems like a ret-con will be acceptable
I have been compiling my thoughts and considering the module itself and I have come up with two to start. They both keep everything exactly the same up to the creation of the Zombie Trolls, Summoning of Drommacus and the Spectre: and changes the arc of the story before going to the village.
The short version of 2 options:
1) Ke'Sha never created jujus or the wight. the bargain with Drommacus was for something unrelated to souls. he gets a several spell slots back (from where he is now) and the party is in the same place but simply arguing over Drommacus' bargain
2) The jujus and wight are from Drow encountered in the cave. Drommacus' bargain was not for souls. everything else the same (spells, etc), everyone is just suspicious of Ke'Sha. But now he can truthfully say he didn't hurt innocents, which might help settle the in-game discussion
I don't want any of this to feel like a cop-out to anyone. If any of the players feel this is unjust, speak now.
If anyone has a 3rd option (like the omission of Drommacus in general) that they prefer, let us know
The reason the spells are still limited is because a dungeon module like this is always about resource management. The spell balance for option 2 is the same to account for the efforts in taking the Drow. Nobody has an infinite tap of power or ability, things have a cost and provide a benefit. It’s part of the game.
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Rationale:
[Providing rationale because I have an analytical mind (too much so it seems sometimes) and take things like this seriously... again probably too much so sometimes. To some of you who know me irl, I'm sure this comes as no surprise.]
Yes, there are Drow in the area. The cavern surrounding the mouth of the snake head leads to the underdark (around the 'hill' in the middle of the image). In fact, there are
several drow corpses in the Labyrinth (not undead, just dead). Of course neither the party nor the players is meant to know that at this point, but maybe it will help. Also, none of them have 'those fancy cloaks', but there is some loot on them.

going down to the area around the 'hill', or things wandering up from it is not out of the question. It could be possible for Ke'Sha and Allikhain to run into a few in the tunnels between camp and the dungeon entrance while ‘searching for raw materials’. Although a bit of a stretch, it is not impossible, and it is the simplest solution for that option.
Drommacus:
He doesn't need souls. His bargain could be reached without that, he accepted that because it was the option he liked most out of what was offered and he tried to negotiate for innocents. Ke'Sha gave in to his counter offer, but he would have accepted a higher volume of 'less pure' souls like those of monsters or evil enemies. Not sure how the rest of the party feels about that though, so maybe we should just stick to 'magic loot' or 'favors'
Drommacus also doesn't know that the party is about to go explore a large dungeon complex, so he didn't ask about magical items or spells.
He didn't need treasure or undead servants, so he discarded those options. But he might be interested in:
-Magic items or spellbooks they find along the way
-A future favor or the casting of powerful long-duration spells by Ke'Sha for his benefit
-Help defeating a rival in the abyss (for after the adventure, probably)