Took Clarke long enough to not be horrible and take responsibility. I'm guessing since mom smashed the radiation chamber, Clarke is going to go out in the black rain to test it next episode. I'm still not clear how they plan to make everyone else a Nightblood; I don't think Luna has enough bone marrow for that.
So why did the cultists leave the bunker? The world was still radioactive, so it must be that they ran out of supplies. But how did they survive since they would've had no evolved tolerance for radioactivity? In any case I suspect that bunker isn't going to be too useful for hundreds of people to call home for the next few hundred years.
On a pragmatic level the showrunners are not going to want to have next season set in a bunker the whole time, so I think this bunker idea is going nowhere.