Unfortunately once they're gone it would be difficult to bring them back. You can still see them hanging around by the shops from time to time. If your patient you could wait for someone else to move out and then buy whatever villager from someone (Unless it was a high tier character) I feel your pain, in WW my two favourite villagers moved out, Twiggy and Wolfgang. Twiggy moved several months before Wolfgang but I remember being absolutely deverstated by this.