This is reminding me of all the depressing endings to Lost Belts in Fate Grand Order...where a resident of that world that we bonded with has their final moments before disappearing forever.
Characters only die if they are forgotten. In memories, in fanart, in the collective imaginations of those care, they will live on, and so will their love. The author has done his part; now it's up to us to give them their happily ever after.