Great thoughts across the board here.
We will probably introduce a rule that once the suspect threats are neutralized, the game will end. This is mainly because yeah, the cleanup in active shooter kinda sucks. Alongside this, civilians fleeing for their lives in certain situations would be ideal, cause I'm sure there will be a lot of jumpy players who will need to learn a lesson on threat identification!
The goal of the mode is to make the suspects really difficult, and ensure that civilian casualties will be guaranteed if the player doesn't clear smoothly and attentively.
If they're killing everyone and you're way too far away, well, that's a failure on our part to make an engaging mission variant. That said, we're always thinking of ways to improve our modes. So this is great reading.