The occasional long-lived TV series undergoes a complete turnover in the starring cast over the course of its run. A prominent example that springs to mind is Law & Order, which, with the departure of Steven Hill in its 11th season, no longer had any of the main first-season cast members.
Can anyone think of any further examples? I’d be particularly interested to know if this phenomenon has ever occurred with sitcoms, as opposed to dramas.
For the purposes of this question, let’s consider only fully scripted works of fiction (i.e., no documentary series, educational programs, game shows, reality TV, news programs, etc.), and only those which are intended to have a steady cast playing recurring characters (so no anthology series or movie-of-the-week shows).
Also, have any such shows had a turnover faster than Law & Order’s 11 years?