Riki and Rin have chosen to ignore Kyousuke's pleas to live on and prepare to move forward without their friends, but can they really save their classmates? Before this can even be considered, Naoe needs to overcome his narcolepsy.
To do this requires him to revisit the very start of his troubles - not just the accident that claimed the lives of his parents which went on to cause his first bout of narcolepsy, but all the way through to his birth and the innate understanding that "to live means to lose". Accepting that living your life means losing things dear to you gives Riki the confidence to awaken and face the difficulties before him, and thus he and Rin can go about trying to rescue their friends from the bus crash threatening to snuff out their lives at any instant.
Between their hard work and quick thinking, the pair manage to extract all of their friends aside from Kyousuke - first, from the immediate danger of the bus, and then up the hill to outright safety. With Kyousuke's bravery having led to him plugging the coach's fuel leak with his own body, he's the last to be extracted, and not a moment too soon... although this trauma leaves him in a coma, we're ultimately left with a happy ending as the group are reunited and given the rest of their lives to look forward to.
While sudden happy endings often feel less than satisfying in anime, Little Busters actually felt agreeable in this regard - Kyousuke's sudden transition from coma patient to fighting fit aside (which was at least in character), the rescue of the group by Rin and Riki felt like a believable and worthwhile outcome to what had gone directly before. Whether this strong ending is enough to justify everything that went before is certainly arguable, and the story as a whole still doesn't fit together in as satisfying a fashion as the likes of Clannad, Refrain did at least provide some powerful moments to justify all of its setup, even if it's perhaps the weakest adaptation of a Key work that I've seen.