How about an AU spinning off of the end of Season 2 where after weeks of searching, the team reluctantly concludes that Shiro must be dead. But rather than stick together, Keith refuses to accept anyone other than Shiro as the Black Paladin (including himself) so when the team tries to sort out who will replace Shiro, Keith decides to leave. He somehow figures out how to make himself look Galra and he sets out to infiltrate the Empire, figuring he’ll just have to take down Zarkon on his own.
Meanwhile Pidge decides if there’s no more Voltron because they’re down two paladins now, she has no more reason to stay. She also leaves, intending to search the universe for her brother and father, though she at least says goodbye before she takes off, unlike Keith. The team is down to Hunk and Lance, Coran and Allura.
Lance seriously considers just trying to go home, just giving up on Voltron like everyone else seems to have, but as he’s loading up Blue, getting ready to head back to Earth, he looks back and sees Coran and Allura watching him go, looking completely defeated. And suddenly he just can’t leave. He misses his family, sure, but Allura and Coran have lost so much already, he can’t bear to make that worse. Besides, he knows that if the Galra aren’t stopped, his home and his family will eventually be in danger, and he can’t live with himself knowing he’d be at least partially responsible for that. He stays.
Hunk was just going to stick with Lance, because they’re best friends, no matter what Lance decided, but he’s painfully relieved when Lance changes his mind and decides to stay. Allura and Coran are pretty much crying.
So the four of them become this tiny little resistance all on their own, sometimes working with the BoM group, sometimes on their own. They can’t form Voltron, but they’ve got two lions and a lot of gumption, and they’re going to do whatever the heck they can to stop Zarkon and the Empire.
Then one day, maybe years later, while Lance and Hunk are sneaking into a Galra facility on a mission to get supplies, info, and to cause some damage, they stumble upon a Galra soldier trying to release a very familiar-looking man who is floating in some sort of healing pod. Hunk almost attacks the Galra but Lance stops him, saying “I’d know that mullet anywhere.” A very surprised, very purple Keith looks up at them with wide eyes.
(Oh, and Pidge and her fam are totally there too. Keith and Lance get into a shouting match that draws their attention and leads the Holts right to the rest of the team. Pidge and Matt end up being the ones to figure out how to release Shiro from the healing pod, though they have to use Keith’s hand to actually activate the system. Then there’s a brief argument over how the group is getting out of the Galra facility and who’s taking Shiro where, which Lance and Hunk win by virtue of the Castle of Lions being the biggest ship, and the only one with healing pods.
Pidge’s dad marvels over how unlikely it was that they all managed to be reunited at the same time like that, but all of the Voltron Lions look very smug somehow for the next few days despite the fact that their faces are solid metal and can’t show expression)