They’d eventually both learn to swear, sort of.  Joyce has a G-D moment in next year’s reruns, before immediately becoming Rated G again until the sixth year of Dumbing of Age.  Both times are pretty important moments.  She still swears pretty sparingly.

Walky would have to wait until being rebooted in Dumbing of Age to unflinchingly swear.  Honestly, it never made much sense for him to not swear.  He only doesn’t swear because he’s being propped up in the Walkyverse as Joyce’s Inevitable Boyfriend.  In the Dumbiverse, he’s not a rampant pottymouth, but he doesn’t care not to swear, either.  I feel that’s more true to him, being a devil-may-care snarky goofball.

(That said, I kept “Walky doesn’t swear” as an aspect of his dialogue through to the end his Walkyverse appearances, since that’s a rule of that iteration of the character.)