Lucky doesn't have to come back just for Liz though. Like I said, his mom, siblings and son are on the show. Both he and Liz are major characters in their own right.
There are characters I don't like but know they are popular/integral to the show. :side eyes Sam, Maxie, etc etc: I think Lucky is one of them too.
(I am an LL2 fan, but never cared for the permanent lock stuff myself. I've never re-watched that vow/wedding episode, it was sheer cheese.)
I've seen people saying he doesn't care about her, he's manipulating her, what have you, and while he is manipulating her I think it's pretty obvious he wants them to be friends.