A story that could have been given to Jenna post Bobby would have been why she seemed to resigned to settling for being second choice... first with Bobby and then with Ray.
I think both SK and PP were under contract and the showrunners couldn't figure on anything else to do with them
I think that Ray was written into a certain role by necessity.
His brothers, JR and Bobby were capable businessmen, and Donna was well accomplished.
Someone had to be...less accomplished, and Ray was never really allowed to develop as a businessman
JR once said something to the effect that "he's a foreman and that is it"
JR wasn't being mean-spirited, it was just the narrative.
Donna didn't seem to object too strongly.
I have wondered about a Bobby/Donna pairing
It could have led to some great drama involving all the characters
JR being concerned about such a strong alliance
Ray and Pam being ...really unhappy
Cliff and Jeremy W manipulating the situation
Ray and Pam did have a similar story - both with flawed fathers (although Digger seems to have been a loving father
despite his issues), absentee Mothers, Aunts who were there for them and Ewing influences.
Would they have rekindled? Probably not, but it was a possibility
Having said all that, I liked Ray and Donna.
I always thought that they were an underrated strength in the show,
doing a great deal to stabilize it