About leaving Takuro to the roaches, I tried that as well, it would strand the player's progress in the game because if Takuro died to the roaches he would not leave behind the vinegar which he does, so there will be no way to get the Iron Gate Key
I tried to find the vinegar but to no avail
Edit: So the way to find the vinegar is step over Takuro and get it, also you're right leaving him to the roaches has got nothing to do with his fate on whether he lives or dies