By this point neither the character Ray, the character Jenna nor the couple Jenna/Ray worked. (see No.2
http://www.tellytalk.net/threads/ray-and-jenna-season-10.12379/page-2#post-363679).
After 8/9 years the producers refused any longterm planning which was so essential for a saga like Dallas. Storylines spanning two full years, like Bobby Pam breaking up/reconciling seem impossible at this stage. Obviously tptb decided to produce the show as long as possible despite a detoriating quality because Dallas was selling internationally well.
But Dallas was beyond saving - the old cast was tired, no more location shoots, the budget was restricted annually, cast members decided to move on or were let go, the structure of the show (feud Barnes/Ewing, fight for Ewing Oil was gone) ceased to exist.
It's a shame that Katzman never planned how to send of the Ewings into the sunset.
He knew the TV business, that further cutbacks were unavoidable. Knots Landing managed to reunite Val and Gary by the series' ending, even Dynasty reunited Krystle Blake in their reunion.
Jenna/Ray as an Intermezzo? Well, if it has to be, why not?
But ending the show with them raising Bobby's (!) child in SWITZERLAND (!) (and Donna raising Ray's child in Washington) that's a blunder which could easily have been avoided.
E.g. when they wrote out Donna, let her plane crash towards Washington and reconcile them a year later when they wrote out Ray.
It should have been a service to all longterm fans to give some closure at series' end for SueEllen& JR, Donna&Ray and Bobby&Pam (who was open to this scenario, why didn't the shoot a scene and use it whenever they decided to quit?)