I hope she will return. Best Yonko Pirate Crew and best Yonko character so far. Also, this is Oda. He left some plot points open that will be addressed in the future (three-eyed tribe, Loki, Mother Caramel and underworld, etc.)
We know Mother Caramel had ties to CP0 and the underworld, so it makes sense to dive deeper into the CP0-underworld-schemes with BM together. Since Shanks is rumored to be king of the underworld, he will probably play a huge role as well.
I just hope there is a twist behind her backstory. Like Mother Caramels soul taking over Big Moms body or something related to her DF. "Big Caramel Mom" would make an interesting villain, but that's just wishful thinking.