I voted never, but it really depends on the reason for missed sessions - some reasons are more legit than others.
For example, missed sessions may just be a symptom of legitimate boredom in a campaign, and if so, you shouldn't necessarily wait for several missed sessions to pass before doing something about it.
For example, missed sessions may just be a symptom of legitimate boredom in a campaign, and if so, you shouldn't necessarily wait for several missed sessions to pass before doing something about it.