As we mentioned, Gail Fisher left Mannix at the height of its popularity. The only other Mannix actor who had more screen time than her was the show’s star, Joe Mannix. And yet, the series didn’t miss a beat after she left.
Why did gail leave mannix?
Because the script called for Linda to be written off the show. This was a storyline decision made by the show’s producers. They wanted Linda to sail away in a boat, never to be seen again, with Mannix watching her go. So they knew they’d need a replacement actress to play Linda.
Source: Internet