Because
Dynasty ended on a cliffhanger in 1989, it was decided (just two years thereafter) to briefly bring the show back to tie up all the loose ends. The result was
Dynasty: The Reunion, which many consider to be quite inferior to the original. "The way we were cut off was a disgrace," noted John Forsythe, so ABC gave the go-ahead to a its production.
Producer Aaron Spelling said: "Beethoven can leave a symphony unfinished... We don't think we could do that with a soap opera." Because the majority of the cast was eager to give the series closure, they each returned at "slightly reduced salaries", and filming relied on location shoots instead of the expensive indoor sets of the original's heyday. Between the each of them, Joan Collins and Linda Evans had forty-two costume changes throughout the four-hour miniseries.
The majority of the original cast (from the final episodes at least) returned to reprise their roles. Al Corley stepped back in as Steven because Jack Coleman had to decline due to scheduling conflicts with his current series,
Nightmare Cafe. There were no on-screen explanations given for Steven's second change in appearance. Gordon Thomson, who played Adam, was busy on daytime's
Santa Barbara, which led to his replacement with Robin Sachs. Michael Nader, who played Dex in the original, was tied up with
All My Children at the time, and his character was written out. Kathleen Beller came back as Kirby, and Maxwell Caulfield popped in as Miles Colby.
I couldn't comment on the plot because I haven't seen it all myself, and I won't especially if you haven't seen it.