Hmm... Halsin joins you with intention to remove Shadowcurse, so I don't think it is unreasonable to expect players to pay attention to him, if they are interested in removing the shadowcurse. If I remember correctly it wasn't exactly him who initiated the quest but an NPC in the Last Light. I think it is fine that the game requires active investment from players for some things to be found, even major choices like that.
It is interesting that you didn't get UI popup that someone wants to talk to you... perhaps it doesn't apply to the followers? If it doesn't, than I think it should.
However, I have issue with the other side of the issue - somewhat unintuitive points of no return. Personally I struggled more with the first one (what exactly will I be cut off if I move on?) I found implementation of those to be very heavyhanded and very vague at the same time - not great.
It's very easy to miss if you listen to Jahiera and talk to her friend, then get immediately tossed in a battle you can lose.
Thats how I missed it.
Plus you need to bring Halsin along. I hate him.
