Who will it be?

An accident in which one dies and changes the lives of all the four.

Gunjan - in my reckoning, least likely. If she dies, no repurcussions of their night together. Sam will be devastated, will probably lose his mental balance, if he doesn't kill himself. If he feels himself responsible for her death, he WILL probably kill himself. Mayank and Nupur will be grieved, but they will carry on with their individual plans, as no one has to take care of Samrat, he's not their responsibility. If Nupur blames Samrat, major issues between Samrat and MN, and distances. MN finish their respective courses, return after leap ... what issues between them and Samrat? Samrat will probably have retired deep within himself ... or become a playboy again with a vengeance, thinking that he is destined to be alone. They try to reform him - maybe enter Sanaya in a new avatar?

Samrat - the most cliched and hackneyed option, so could be possible. Or not - CV's have actually avoided a lot of cliches for SG. But the most cliched - Sam dies, Gunjan pregnant, again two options, MN raise the baby as their own, G lives with Nupur, or G decides to raise the baby alone, knowing her, this one is very likely. Again the impact for Mayank is minimal, for Nupur, slightly more. Unless Mayank gives up the US option and stays back with Nupur and Gunjan - why should he?
Sam dies, Gunjan not pregnant, but devastated, she decides to complete the movie and make her life on her own. That is IF they continue with Neil. Her life changes, impact on MN again is minimal.
After leap, M returns to Nupur, Gunjan settled in some career, with or without child ... this is really not going anywhere. Because Gunjan can handle Sam's death, especially after their night together. That has completed their love story and will be her strength.
Again, can't see much impact on MN here.

But the track is supposed to be a MN track ...

Mayank - maximum impact on Nupur, she continues with her scholarship, SG carry on with their lives, becoming a support system for Nupur. Again if Sam is driving, he feels responsible, and this solidifies his support for Nupur.

Nupur - maximum impact on two people - Mayank and Gunjan. Mayank devastated, and he was more upset than Nupur about the impending separation. He would carry on to the US, and return after the leap.
Impact on SG - especially if again Samrat was driving. Samrat guilt ridden, Gunjan devastated at losing the mother figure in her life. Distances between SG, may lead to separation, if married, would affect their marital life. Samrat would be unable to support Gunjan fully because of his own guilt. Gunjan would be unable to comfort Samrat fully because of her own loss. Major issues here. But this becomes an SG track.
Mayank comes back and tries to get SG back together, he has lost his love, he doesn't want the same thing happening to SG.

Again it's supposed to be an MN track - if one of MN dies, where's the MN track?

So confusion still reigns.

Unless it's not the story that is dictating who dies, but the exit of the characters that is dictating the story ...