okay, so. metanarrative analysis time. for this quality to actually land as it should, even for non-vanguard players, the story whose ending gets ruined needs to be very firmly post-Irem. otherwise, you could take this deal with no consequences by just doing the other story first. (i mean, you probably could anyway, unless said story is also a repeatable carousel. but it's not ideal if someone can do that accidentally)

irem isn't *that* late in the gameplay progression, ever since evolution was downtuned a bit, but it's still not particularly early. either the content boundary would need to be pushed a good ways ahead, in order to statistically guarantee it, or it would need to directly depend on having completed Evolution. both seem rather far in the future