Hmmm. Good question, actually. Levesque was a major part of the PQ's rise as it was. It would highly depend on whether they found another many with hims charisma. If they did, it makes little difference. If they don't, it takes longer to get the separatist movement off and running, and no referendum in 1980. That has lots of butterflies - the Constitution, Meech Lake, Charlottetown, a bunch of others.