Assuming that by "consquences" you mean the "Defend this settlement" quests that pop up and then "Fail" if you don't go there, it's less dire then the game implies.

"Failure" is simply "You didn't go there to help". As a result the settlement may be completely untouched, damaged, or completely destroyed based on off-screen dice rolls and your settlement's defense stat.

So even if you "fail" the quest, you can take a look at the settlement's stats to get an idea of the damage, if any (though I think there might still be a bug or two in there - the 1.3 beta patch mentions some fixes along those routes)