MessyLife
A due to the political problems that would arise by not stopping the last uchiha from the risk of dying. frankly our hands are tied even if in meta we know things should in theory be fine we cant risk it. any compatent nina that understands what the last uchiha can do for the village and the political fall out that would occure by not even attempting to save the last uchiha none the less a fellow leaf nin. frankly would be suicide and while I understand its unlikely to truely be shinji's downfall I feel like he would be aware enough to do what is expected of him from the village whole a coma is acceptable we cant risk him dying the choice is A and just because we save him does not mean we cant make it clear it's because it's what is expected not what we wanted or could have done instead
A because Shinji will probably lose relationship points with most Character which are here and who will appear ( Gai and Kakashi), if he didn't even try to stop it do note, gai probably knows how strong shinji is and shinji knows this move is dangerous because he saw Gai use something similar, so if he doesn't even try to stop it, Gai is probably be extremely disappointed and might even get angry since lee is direct student, who he is passing his Techniques to basically B highly smells like it will cause a lot of bad stuff, but it's up to you
A we can't be sure of all that happen in canon happen, plus if Sasuke die it will cause problem latter as Sasuke killed Orochimaru, Danzo and helped against Kaguya and company and maybe there will be also problem at his team if don't try to save Sasuke. is not like we wil lose something try to help: if thing are good before we help Guy will intervene if are bad we save Sasuke or at least try so nobody could blame him for not try helping