How many games are there, where, in a situation like at Toriel's house, the player is allowed to just live happily ever after? Especially when the scenario has the protagonist in a place that's cut off from their standard reality, I can not think of one example where the player is allowed to remain in that reality. with the exception of death, or preventing the plot from progressing as you've mentioned here. It's something developers don't do in games, so why expect it of any game? Though I do think he should add additional ending for it, because killing Torriel and then going and living in her house, would be hilariously creepy.

I find it a little odd that you had so much disconnect from emotional involvement in the ending to this story. In my playthrough, I expected there was a way to evade the battle, but had difficulty finding it, and then surviving long enough to engage it, such that I ended up fighting her instead. In a game about how fighting is an easy answer to see, and overcoming battle in any other way is often difficult--even to tell if it's successful--I feel the ending to the game is a good test of the features put forward throughout the game.