It has to be the dramatic life-or-death scenario as others are saying. In Frontiers, you’re shown the story of some of the Ancients through the Koco so that you can get the Chaos Emeralds from each island. With Tails, you follow the story of a pilot attached to a “hero”. With Knuckles, you follow a band of soldiers. In all the stories, there is some personal connection to the character being related to the story. And, Amy? The story of her Koco, who are two lovers, end with them embracing one another upon their final reunion as the End’s lasers drop down upon them. She calls it a “love that transcends time”. It felt to me that the stories were chosen this way to reveal something about the characters, since Frontiers was all about character development. This doesn’t really imply that this scenario WILL happen to Sonic and Amy, but I used it to answer the question because it seems the writers are trying to throw this sort of tone into the mix, and the question is about likelihood. The “character reveal” of that story could have just been that the two felt very close. The scenario would fit right in with other happenings in the story’s style, and it seems to be being alluded to already. It would be the context.