@Orriee: "five-year survival rate", used in chap1, means the chance of being alive 5 years after the surgery. It doesn't mean the surgery is only going to extend his life by 5 years and then boom. If he takes the surgery, MC has 30% chance of being alive in 5 years (he can die before, after 1 or 2 years for instance). If he doesn't, he would die in 6m to 1y.
There is a scenario in which MC can live (surgery going extremely well and he recovers well, although full recovery is said to be impossible), but the chance of it are extremely slim.
With that said, I'd really like the manga to focus on that death flag and relationship, instead of that silly music festival and such... Really don't give a fuck about the festival, the music and all, wish we could skip that part, or that it only takes 1 or 2 chapters top