The main thing to do is find out from your player base why, upon hearing that the next session would resolve six months of storyline they ostensibly cared a great deal about, they responded with radio silence.
Perhaps your players simply became too busy to game any longer. Perhaps they lost interest in the hobby entirely or naturally moved on to other pursuits. Or perhaps the dates/times you normally pick are no longer convenient for group members. Each of those cases would say your basic approach is fine and could work more or less as-is in the future with some logistical adjustments or rearrangement of players.
However in my experience there are some other reasons that might point toward a more fundamental reassessment. Sometimes DMs become more enamored with their campaigns than the player base, mistakenly believing their plotlines to be GoT-style epics when in fact there are inadequacies readily perceptible to the player base but unseen by the DM. Other times, especially when there are family ties between the DM and certain members of the group, a perception takes hold (rightly or wrongly) that those members are advantaged during the gaming session with other members being correspondingly disadvantaged. Either way disaffected players will often respond with radio silence rather than "checking in" and risking a dialogue about unspoken truths that in their minds would hurt feelings without producing meaningful change.
What I'd suggest is first ending the campaign and then non-confrontationally asking your players for feedback on what they liked and disliked about the sessions they attended. You might even volunteer the sentiment that the campaign seems to have ended with a whimper rather than a bang and you're looking to avoid that in any future campaign you might run. Then, and most importantly, resist the temptation to rebut what you hear in that conversation, even if (especially if) you don't like what your players have to say. Instead thank them for their candor and ask for suggestions on what they would do differently if given the chance.
Hopefully you'll find out the breaking-apart of your group was due to nothing but bad circumstances. But if there are deeper issues, learning from them might make a big difference in your next campaign. Best wishes and good luck.
