Main quest disappearing, can't get to New Game+

I'm having problems concerning the mode New Game + in Torchlight 2. I would really like to proceed to that mode and or to Mapworks, but it seems that every time I go to The Minehead or defeat the final boss (Netherlord), the main quest disappears and then you're just stuck at the game. I've tried different characters and still end up with the same problem.

I already finished all quests main or sub but still talking to Felicia or to the robot leading to Mapworks won't do anything. I'm playing v1.16.5.3 and I'm only playing single player mode game.

You should update your installation to the latest patch (1.19.x.7). This issue was resolved in the 1.17 update (found via the patch notes for 1.17.x.14):

Some players stuck in a state where their quests will not advance, or the final quest will not complete, allowing access to the mapworks, should be resolved.

1.17 also adds two new pets and some fun new phase portal challenges.