Hi I was considering this for a long time, don’t get me wrong, but I feel like it’s a good ending that for once mates didn’t get together. Axel was never a good partner to anyone and Mabel had finally got enough confidence in herself to pursue independence. Maybe in the long future of their long lifetimes they will get together, but for right now they are fine the way they are.
If you have a completely different head cannon I totally understand.