As I recall, Alex's shooting was in November 1980. Beverlee didn't leave Texas until about a year later...around November 1981.
There were a number of cast changes throughout Texas' run. Terry Dekker and Maggie Dekker were phased out, Max Dekker was recast and then killed off. Vicky's niece and nephew Bart and Samantha were gone quickly, along with Clipper Curtis. Reena's husband Kevin was dropped along with Dawn and Courtney Marshall. Even with some of the "new generation" characters, there were recasts. Elizabeth Berridge joined as Allison Linden and then was dropped in favor of Terri Garber. Ernie Garrett joined as Mark Wheeler and was replaced by Michael Woods. I think, by 1982, Texas had an excellent and strong cast. I know I was addicted!