system
Given the following post, respond as if you're commenting on Reddit:
human
[Undertale] Spoilers for cannon/true pacifist ending

A young child is the ambassador of the humans. 

A young child who has shown powerful skills of diplomacy and a skill for thinking on their feet. 

BUT... The underground isn't as large a place or complexly political. 

If Frisk chose to go with Toriel is she accused of kidnapping? Does that sour negotiations? 

They all took off without actually contacting any specific leader. How would humans react to the monsters? Is the history of monsters v humans widespread? Or are people caught unawares? Are Alphys, Undyne, Papyrus and Sans fated to finding only violence? Certainly Sans and Undyne are clever and Alphys is brilliant. Papyrus has confidence but.. really.. Little else. Right?

The king is quite optimistic, kind, and powerful. And.. naive. Does he truly think everything will be fine with them all running off? How naive is he and what danger will he most likely face?

Frisks first goal ought to be to find family and then political leaders. How will they respond? How long has Frisk been away from home and how positively will leaders respond to the arrival of monsters and the return of a child?

I beat the game with smiles and tears. Laughed even. But... I really do think that there are few positive things facing this happy crew.
gpt
If you pay attention to the credits, you can see that one way or another, it worked out. Sans and Papyrus got a car. Toriel opened a school. Mettaton went on tour. And that's how it is when you have a lot of determination and a little caring. The how isn't always important... but there are worse methods than to start by sharing an incredible tale of courage and friendship.

Frisk doesn't have any home or family to go back to. They were so alone no one cared if they lived or died. That's why they went to Mt. Ebott: to disappear. That's why within minutes of meeting Toriel, they started calling her "mom." And that's why they let her adopt them in the end.

Frisk's friends were just the first wave; if you go back and talk to the other monsters once the barrier is broken, they are nearly all preparing for their exodus from the underground.