Honestly, Marlon and Kent would probably organize the villagers.
Hotheads like Alex, Pierre, Abi, and maybe Shane and Penny would step up, as would Willy and Gil.
Gunther and Lewis would pack as much junk onto Willy's boat as possible, but there would be an argument, and many precious artifacts (and statues) would be left behind.
Lewis would forget where he left his shorts.
The more creative and innovative villagers, like Leah, Maru, Robin, Emily, and even Clint would fashion their own ways of fighting back.
Haley would learn she's surprisingly good with a firearm.
Seb would finally see the chance to leave town, and dip on his motorcycle.
Kent would give George a shotgun. Vince would have one of the farmer's slingshots that he left laying around town.
Marlon would attach a flail to Jas' jumprope.
Everyone would drag Gus along because he's the town's ol' boi.
Maru may or may not have armed Demitrius. If not then he might either improvise something from his lab, or tag along. For research into this biological phenomenon.
Sam would use his skateboard, and maybe the farmer's other slingshot. (Trucks hit hard)
And those that don't go with Willy to the Fern Islands, or Ginger, would go with Pam on the bus. So likely Lewis and a few others.
Most likely to die? Marnie.
Most likely to survive? Evelyn. The junimos love her.
Not sure what a few others would be doing.