Agreed. I should point out that the druid initiated the conversation with the anti-paladin, who was just going to attack the party, and suggested sacrificing herself so the party could live. I rolled a really high reaction roll from the anti-paladin, even before adding the druid's 18 charisma bonus, so he agreed. None of this was planned, and the players directed this interaction as much as I did.
Still, these things make me uncomfortable because you can never tell if everyone at the table is perceiving this situation the same way. I mean, here I was planning on a big battle in dark castle between the anti-paladin (and his men-at-arms) and the player party, and I ended up with the druid discussing which room in the castle to use as a nursery.
It was a weird night. But if anything, it underscores my point that the DM never knows what the players are going to do.