Having XXX marry XXX is a disservice to her character
Having Mei marry Joel is a disservice to her character.
I am kinda glad that Mei didn't end up with Joel, if she did:
- She would have to be Jewish, just to make Shirley happy.
- She would be marrying a man still in love with his ex-wife.
- Her in-laws will still be very close with their Jewish ex in-laws. This is obvious in the hospital scenes. It is hard for her (and her family) to integrate with Joel's family and not to be seen as outsider(s).
All of these do not fit into a confident, independent character who knows what she wants, and pursues it regardless of what anyone else thinks.
Also I think Mei is smart enough to realize the three points above and ultimately chose to leave and not keep the baby. I think only someone air-headed like Penny Pann will marry someone like Joel and get entangled with his ex-wife and her family.
Last but not least, Mei being in the family will be dangerous for Midge's career. In her gigs, Midge often talks about her close family, which will soon include Mei. And I don't think a dangerous and secretive mobster family like Mei's will appreciate that.