My group of friends and I have been running a D&D 5e campaign for over a year now, but as time progressed we have found more and more issues regarding scheduling to the point where we are on the verge of cancelling the whole thing entirely. Currently, our group is composed of 3 players (with a fourth one having already left the game, his character forever stuck as a GM-controlled NPC) with Sunday being set in stone as our definitive game night. However, one of the players has now become unavailable at that date and is now only reachable on Mondays, a day when no one else can play. Kicking her out of the game would be the easiest solution, but I feel like that would create more problems than it solves due to her being one of the most important characters in the game (playing a bit of a main protagonist role) and the fact that it would diminish our already small group to only 2 players.
I feel like we really have been backed into a corner this time. We could barely play our game when everybody was available on Sundays because of last minute appointments (which were far more common than I'd like to admit), and this will probably further disincentivize people to continue playing the campaign. So? Does anyone have any ideas on how to proceed?