"Is the barrier meant to keep humans out, or monsters in? The archmages are so far as I know all humans."

"The barrier was built with the intent of keeping monsters in, not keeping humans out. Humans have fallen through previously. However, it was also intended to prevent us from sending out various non-monster hazards, so it in fact prevents humans and inanimate objects from leaving."

"Well, they're archmages. I would be a little surprised if they had trouble with this. But if I instead receive a Sending instructing me to make my soul unavailable through some other means I will have in mind that this was a plausible outcome."

"A Sending?"

"Your 'cell phone' seems a little like an artifact of Sending, only the spell doesn't require the recipient to have any particular object on them and doesn't work by sound, they would just cause a short message to reach me."

"That sounds very useful. Could you cast it, too?"

"It's fourth circle, I'm not powerful enough."

"Oh well."

Up ahead is a leaf pile with another little star.

"There's another one." He visits it; the last was harmless, a heuristic that fails with mimics and if considering dismissing a food taster while possessed of enemies but good in other situations.

It's warm again, and it plausibly would heal him if he'd gotten injured.

If Blai were to die, or otherwise encounter a serious problem, would he want the option to return to this light instead of the other one?

...can he tell if he gets to pick whichever light or if it's just replacing the first?

It would replace the first if he picked it.

The likeliest way to need this service if in fact the service exists at all would be if Toriel were untrustworthy. So no, he doesn't want to replace his old one with one nearer her house.

Well, then he doesn't have to.

They take a brief turn south, then continue heading east.

There's a pair of doors in the wall, with no outer handles. Separating them, and blocking the way east, is an unsubtle false floor.

"The fastest route here involves both of us going through the false floor into a pit."

"How long a fall?"

"Same as from here to the ceiling. There's an Underground-wide spell up to make falls safer these days, but I'd understand you not wanting to trust that. In that case I'd go in and hold the door for you."

"Do they work for humans?" He looks up at the ceiling.

"Yes. I'm guessing it was easier to build that way."

"If you'll go first so I can have a look at the drop I am amenable."

Toriel walks onto the false floor and falls through. The drop is as she described.

He follows.

He is uninjured. There's two ramps heading out and Toriel has picked one.

She seems like a decent sort but she might just be playing a longer game than the flower.