Ending the entire show on a cliffhanger
That was just a ridiculous ending to the show. Although it was pretty obvious what was going to happen - Caroline would not have married Randy and would have ended up back with Richard, as he came back for her and loved being a dad more than he had expected - meaning he would have been more open to the idea of having more kids with Caroline, which would have solved their entire problem. Del and Annie would have admitted that they actually were falling for one another.
It wasn't really unclear at all how things were going to end up. It just would have been really nice to see it. They literally could have wrapped all of that up in a few extra minutes, rather than ending the entire show on a cliffhanger.
And obviously, now it's too late for anyone to do anything about it. The actors have all aged nearly two decades, and plus it's not like this show was Friends or Seinfeld - there simply wouldn't be enough demand for them to film one last episode for closure.