I approached my games as an episodic adventure TV show with each episode/gaming session being its own self-contained story and plot. There would be some 2- and 3-parters when wanting to tell a larger story but I knew my group and I knew that months-long campaigns would get bogged down by some of them not making it to game night. Also when one of them couldn't make it, we would still use the character as a non-decision making NPC, so the party didn't miss the damage dealing/spell casting that they were used to. This way those characters also kept up with the XP gains of the rest of the party.