I really bet that there's a ton of old, untranslated Touhou fan book waiting to be unearthed and translated in the future which could be a good reads, and I wish more like this really should've keep coming.
I guess Reimu could always become an oni by drinking from Kasen's drinking box or even just become a hermit. So there wouldn't be any need to worry about Reimu dying first if they get in a relationship.