Judith Michael's Deceptions was published in 1982 and a miniseries based on the book came out a few years later. The sequel, A Tangled Web, came out in the early 90s. I haven't researched too deeply into the motivation behind writing a story that ended with such finality, and I'm not sure I'd find it online anyway. I'm reminded a bit of a story told by another author, James W. Hall, at a signing over 20 years ago. Details are fuzzy, but the gist was that publishers are more receptive if a story they're behind has a sequel. Whether A Tangled Web was written out of financial motivation or because a rampant plot bunny took control, I don't know, but once I learned of its existence I had to read it.
I'll warn you, the book can be a bit hard to follow, mainly for the grand use of flashbacks and deus ex machina. We leave Sabrina in Deceptions taking over for her departed sister; she and her brother-in-law fall in love and return home as though it had always been that way. Web opens about a year after the twin sisters switch lives, and Sabrina is clued in to a look-alike spotted in Europe. So Stephanie, who hedged on wanting to switch back, could be alive after all. Dun dun dun!
Here follows several hundred pages of backstory, which explains that Stephanie and her lover Max survived the explosion on his yacht, how she suffered amnesia, and how they hid out in France while Max resumed his dubious business practices. Sabrina's backstory, interwoven here, covers a number of side-plots that seem superfluous as you're reading them (college finance scandal, troubles with a grad student), but they happen to prove Sabrina's investment in her new marriage and family. While she keeps some remnants of her true past visible, her decision to sell "Sabrina's" antique business coincides with the discovery of her presumed-dead sister.
Probably the one flaw I found with the book is best described as the Annie Wilkes moment. Remember in Misery how Annie rants that Paul can't magically revive Misery because in his last book she was dead and in the ground? Deceptions had a similar problem - there are funeral scenes, and there is a body. A Tangled Web attempts to explain this with a guest on Max's yacht who (surprise) happens to look like Sabrina/Stephanie. An explosion would definitely have messed her up, and the ex-husband who identified her barely looked at the body. I guess, too, nobody bothers to confirm with dental records in Europe. Problem solved.
You get quite a bit of backstory in this novel, too, in the event you read Web first. As sequels go, I found it entertaining and I did like revisiting characters. Some might have the ending figured out, but I have to say it genuinely surprised me.