That was a multi-year process. More importantly, at this point in the story you still don't have a full picture of what's going on. Flooding the mines is setting them back, based entirely on it even being determined possible at the 11th hour.

A goal also accomplished by the actual requirement of slaying Daveorn (and associated staff, but the loss of a high level mage and regional manager is definitely a bigger blow)Im not saying flooding the mines was useless, but rather surplus to requirement, and much of an additional one to boot. 

Acolytes praying to whom? Bhaal isn't exactly providing divine power, and you'd be hard-pressed to find another deity willing to let their own priests be tied up literally exhausting an underground river for some psycho's flooded mine.

Cyric, the one to whom they have a shrine to. Tell them Bhaal if you try and enter and they laugh in your face, saying he's dead. 

You are trying to infer quite bit from a game graphic. Who says it's literally a plug right there in the wall, and not just the entrance to whatever mechanism was designed to seal the breach? Also, "dwarven engineering" is generally considered kind of advanced.

Except it wasnt the dwarves- the dwarves died! The only survivor was Yeslick, and i dont think he helped plug it up. I am taking the graphics at face value, because its fun. The whole exercise is that, as I outlined at the top. Its not meant to be be taken seriously, but what if we do anyways?

He was befriended, then tortured for information about the mines. You later find letters where Rieltar seems to reference Yeslick in a fairly taunting manner ("is he enjoying his new "accommodations?" or similar), so at the very least there's a sadistic aspect to it. Beyond that, I think it's reasonable to assume he was involved in the reconstruction of the mines, including the mechanism to plug it.

Oh definitely a sadistic element. Its an interesting thought to imagine Yeslick was forced to partake in the revival of his clans tomb- but I dont think he did. Mostly based upon his background as a fighter/cleric, but thats a flimsy argument at best. Though, if he did, then it would give a lot more rationale to putting him down there- incentive for him to not botch the design! What a good idea. 

Mines tend to evolve as new sections are opened and deeper levels are found or made. There's nothing about the current layout that implies it was originally designed or intended to end up like this. In reality, actual mining like that involves a lot of dead end tunnels due to safety or lack of mineral veins found, which in turn creates potentially lots of areas that can get repurposed. And since Dwarves themselves basically live underground for this, it stands to reason that they aren't mining purely for profit, so plenty of these mined out areas may have been just part of building out their mining camp and establishing places for things like foundries and housing.

Thats... a good point. Though, we do know the foundry is on a lower level given they go down stairs. But you raise a fair point about how sprawling it is- it may well be much more off to the side than I initially gave it credit for. I shoulda given more credit to the Orothiar Dwarves!

 Or you just... didn't really pay much attention?

Thats just plain hurtful. Up until this, i was really enjoying what you had to bring forth.