I actually managed to fix it before looking on this board again! I went to Edit Town and Vesper was still part of the household there, so I evicted the household from their house and then immediately moved them back in. When I made them the active household again, they were both alive! The only problem was that Vesper's inventory was erased, including the Death Flower and the Collection Helper lifetime reward, but I got both of those back pretty quickly. Even though I didn't end up using it, thank you for your suggestion!
