EDIT:
@Brad Lascelle, Yeah, why not keep her around since it's Tress doing the voice and I remember liking her character. My only guess for if they don't again would be they only want to change the status quo once every few years and it's not that time yet and/or the writers think Moe is a good character only as long as he's being miserable and being constantly put down.
As
@GlitterCat astutely noted, they were able to marry off Comic Book Guy and still keep him as his socially-distant, sardonic self. His demeanour is partly why Kumiko fell for him in the first place.
No reason for Moe to do a 180 in his personality just because he's got a relationship with Maya. Plus, it would open up some new storyline possibilities for them to mine.
They could have Maya as a fixture at Moe's tavern... possibly implementing some ideas that actually stick as opposed to his many infamous remodels/resets that don't last 22 minutes. And, failing that, they could rehash a Cheers storyline or two.
They could have a Christmas episode where Moe's family gets together with Maya's family for the holidays. Perhaps there's a gag where he expects them to be tiny like her and they wind up being giants.
Moe and Maggie storylines always work. Why not incorporate Maya into the mix and task them with babysitting the Simpson kids one night?
Bart's girlfriend storylines have run long in the tooth. Pull a different spin on Lard of the Dance where Bart feels neglected due to all of his friends having dates for a school dance so Maya takes pity on him and agrees to be his chaperone. Naturally, her cover gets blown, Bart gets depressed but then Moe lifts his spirits by encouraging him not to rush things and to be himself. It'll all work out in the end. It did for him. He could then get Bart to help him out at the bar to lift his spirits before sneaking off to crank call Bart in a role reversal of Bart crank calling him for countless years.
Hell, make Maya a staple friend of Marge. Goodness knows she needs some. Marge, Maya, Kumiko and Sarah Wiggum can form a new social circle.
How much more of status quo Moe is there to mine? I'm fairly certain they've tackled everything. It's time to shake things up. #Moeya