Here's how I remember it all:
Deidre wanted to try something different, but she didn't want to leave "Days." She went in to audition for one of the lead roles on "Our House." The casting people really liked her audition, but they told her she just didn't look the part. She looked too glamorous; she looked like a soap star. So Deidre left, toned down her makeup, toned down her big '80s hair, changed her clothes, and went back a second time. She got the job.
Although Deidre's work schedule was said to accommodate both shows, I remember thinking that Marlena was on our screens less and less. At one point, Marlena helped a suicidal patient off a ledge only to end up falling off herself. She then was in a coma for some time. Then Orpheus kidnapped her, so she was away for a while and had limited interaction with others. When "Our House" was picked up for a second year, it wasn't possible to keep doing both shows. Because of contract obligations, Deidre had to leave "Days" in 1987. So just as Roman (John) got to the airport, Orpheus's plane was taking off with Marlena in it. The plane crashed, and Marlena was presumed dead. "Our House" was canceled after the second season, but Deidre did not attempt to return to "Days" at that time; she needed time off for personal reasons.
In 1991, Deidre was approached about returning. She was eager to return and play Marlena again, but she asked that the writers not give the character amnesia. She didn't want to play an amnesiac. The only problem, she admitted, was that if Marlena didn't have amnesia, she would have moved heaven and earth to get back to "Roman" and her children. Suddenly Deidre had a lightbulb moment. "Unless, of course, she found the real Roman!" She then inked a deal that allowed her to come back if Wayne Northrop returned as the real Roman.
The storyline played out a little differently, though. Marlena woke up from a drug-induced coma in Mexico and returned to Salem to find "Roman" engaged to Isabella. After wandering around Salem and considering disappearing, she finally reunited with "Roman" on the pier. She moved back into their home, but she was having nightmares about being in Mexico. Suddenly, she woke up, and said to "Roman," "You were there. I saw you." She had a flashback of seeing a man in a prison cell. Later, we saw a man watching a video of "Roman" and Marlena together. He asked, "Why is he calling her Doc? And why is she calling him Roman?" The camera moved in on his face, and we saw Wayne playing the real Roman again.
And the rest is history.