I would have actually been a bit unsatisfied if the Diane story went over to Annie. I'm sure they would have changed elements of it, but if it progressed exactly the same way I wouldn't have found it as convincing. In the original show, Dale only knew Annie for a matter of weeks. The story we got with Dale and Diane was able to build on the idea of their decade-long working relationship and bond.

That said, it was a little weird that they seemed to add a romantic element between Dale and Diane that was never there before. So you're probably right that they might have mapped it out with Annie, maybe Wyndom Earle's wife, maybe Audrey...

Both Annie and Wyndom Earle's wife (forgot her name) also would have brought in references to the shittier parts of the second season, which they might have just wanted to wipe from the face of the Earth.