There are consequences and there are consequences.
Lae'zel bangs on about the creche from the start of the game so you don't have to be a rocket scientist to guess that not doing the creche with her in the party is going to have some sort of consequence. Shadowheart is a cleric of Shar who is on a special mission for the goddess so not doing the Gauntlet with her in the party is obviously going to have some sort of consequence.
In my game I killed Astarion, left Gale in the waypoint and dismissed Wyll from camp immediately after recruiting Karlach. I am quite happy to accept the consequences of my actions/choices.
Talking to Isobel after being instructed to do so by Jaheira in no way, shape or form gives any hint that there will be an almost immediate attack or that the attack will have such calamitous and irreversible consequences. We could also add that these consequences are widespread and will affect a number of quests and future events.
