That's generally been true in the past and I would say largely true, but no government can stay in power forever, eventually people will tire.  Also in the 1991 election, I wouldn't call that a right wing split as the Liberals under Gordon Wilson were ideologically similar to the federal Liberals and that election it was 41% left, 33% centre, and 24% right so if you assume the centre would have split evenly, that election had more vote left than right.  Also many Green voters were ex BC Liberals sick and tired of the party but couldn't bring themselves to vote NDP.