How Important Is Bringing Main Characters Back for a Reunion Show?

Background (skip if you don't want to know the background): I'm writing an urban fantasy series with, of course, a long arc for the whole series and multiple character arcs for my main characters. I have a set of *villain spoilers* three characters who will be betrayed by a traitor in their group. They will do something with massive repercussions (good and bad), and will elect to leave the world they're in, for their own good and for the good of society. <br><br>The question of how to handle this always strikes me, because I have two ideas that I'm not sure of. The first idea is, they elect to leave the world and that's where they stay. They're mentioned throughout the rest of the story, but they never show up again. They aren't the main characters in the next books, and they aren't relevant to the plot. <br><br>The other idea is, they elect to leave the world, but they end up coming back sometime. They have one last adventure with their friends, and tie up their character arc. <br><br>My question is, how important is it to bring them back? Do you like to see characters that are integral to the story come back, and have some closure with them? Would you prefer if they stayed away?<br><br>The answer to this will effect my plot, as it changes the arc and ending of the whole story, and whether or not they will be around for other things later. Any thoughts?<br><br>TL;DR: Three of my main characters will do something massive and decide to leave the world. Will you be disappointed if they don't come back?