Don't re-cast Miss Ellie.
And no dream resolution to explain Bobby's revival.
Even if they didn't provide an immediate explanation for Pam's death, turn her absence into a character in itself (as they did with Jock and Bobby). Maybe even turn her disappearance into an ongoing mystery playing out in the background for the remainder of the series -- but don't permanently ignore it like they did.
I also want to find out the tanker truck Pam's smashed into was owned by JR doing secret oil business in the badlands in violation of the fed's rules after the BD Calhoun scandal went down. So JR not only has to run around all season trying to keep this info from Bobby, once Bobby finds out and dunks JR in the pool as per usual, he finds himself in the awkward and ironic situation of trying to keep the lid on JR's clandestine dealings to prevent the family business from suffering any more punishment.
I found the range war plot acceptable, but made too little sense. I want Miss Ellie's reluctance to call in the authorities connected to her fears that something buried on that part of Southfork being unearthed (perhaps something Jock had buried and Wes Parmalee mentioned to her as a kind of "threat" before he'd taken off). We don't have to find out why and what it is until later.
Silly as Sue Ellen's movie was, if they'd done it more seriously, and let it have consequences (like, her eventually releasing it??), I'd be okay with it.
Jeremy Wendell's arrest and removal was totally unbelievable. The very idea that the Ewing brothers, weakened as their company now was, could so easily bring down one of the most powerful and machievellian men in the country was ridiculous (and the result of a salary issue between the actor and Lorimar). I'd have JR and Bobby a few months later mutually acknowledge the improbability of the incident, and we can learn Wendell's fooled them for some nefarious reason. (And then pay William Smithers more money to do so).
The tanker oil spill was fine, and placing Cliff in Ewing Oil just long enough to cause a problem was also good. But Lady Jessica's murder spree, and Miss Ellie's turn as detective, were flawed mostly in their execution -- they could have, and should have, worked!
And that's my issue with the closing seasons: it's the execution and the details which created the problems, not necessarily the general plot concepts. A lot of people complain that JR "turned into a wimp" in the final seasons, but that never really bothers me -- I was okay with JR becoming tired and a wee bit philosophical about his life in retrospect; to me, the problem was the show around him becoming too wimpy, too silly, too campy in tone.
Also, increasing Miss Ellie's role (instead of minimizing it, then ousting her entirely) seems a no-brainer since there were so few original cast members left on DALLAS, especially since she's the one who represented "home" the most. (David Jacobs said several years ago when they were talking about doing a DALLAS motion picture that Miss Ellie could have her own talk show -- or something like that... I might have liked to have seen that in the same year of the oil spill and Jessica's murder spree: Miss Ellie does so well in her appearances on Roy Ralston's local chat show that he and the station offer the show to her as he goes national with his own Coast-to-Coast program... JR and the oil cartel initially thinks this is a great idea, as Ellie could then "spin" things in their favor, but they change their minds pretty fast when Miss Ellie starts waxing too liberal, making pro-environmental comments, etc... And JR responds by trying to sabotage his own mother on the air... Just imagine the possibilities).
And James from London once suggested that Miss Ellie on her deathbed (or at least in the hospital seriously ill) confess, perhaps to Clayton?, that JR is in fact Digger Barnes' son -- a revelation a drunken Clayton later shares with JR and the family, creating an obvious furor and making JR as mean as ever. (It could be undone via DNA testing a year later, if we prefer). The irony being that once they learn Pam has died, ideally by neurofibromatosis, JR realizes he's not only not a Ewing but he's half-brother to Pam! (One assumes Rebecca lied, or wasn't sure, about Hutch McKinney being Pam's biological father).
Etcetera, etcetera, etcetera... So many other things.
Also, if Miss Ellie indeed dies before the show ends, a few weeks later have Ray or somebody observe that someone passed on the information that Wes Parmalee had been located and had recently died up in Alaska or Canada someplace, with no one acknowledging the eerie timing.
Also, just as Ewing Oil is about to go under once and for all, Sue Ellen shows up from Europe, flushed with cash from her new career as independent film producer, and saves the Ewings' much-weakened company for the family -- but places Cliff Barnes in the role of CEO. At this point, everyone is impressed and amused ... except of course for JR who is enraged by the move.
I envision, following one final Ewing barbecue, Sue Ellen sitting out front at night at a lone, cup of coffee in front of her. JR wanders up in his post-BBQ robe, uncomfortably tries to make affectionate small talk, asks her if she's coming in, and she looks up at him dismissively, and says, "Maybe". JR turns to walk back to the house, the camera pulls away from the table, freeze frame and fade to black -- a direct replay of their exchange at the end of the first "Barbecue" episode back in 1978, even the same John Parker melody, but with the roles now reversed.