Yep…
Although I’m not playing them now, took a break again some time ago — felt like I’ve done all I wanted there.
Nope, sadly not.
Yep.
By the way, it was added in the last big patch as a part of the completely reworked treasure system. It has really added a whole new dimension to PvE (there’s also Mythic, but I didn’t like it that much), but it seems like some established players have ignored it and quit.
Sadly, some of that was removed, too:
Like some other bugs, it has never been fixed.
They are available in the wiki, though.
PS That refers mostly to individual mercs and their own little stories, dunno about the main story, though.