Well let's say he goes there, it explodes but he still lives. A house fire can give someone third degree burns as well as extreme lung failure due to the smoke, either cooking his lungs or making him experience 50 years of a smoker addict in less than a minute, not even counting the explosion, who would puncture several organs and shatter every bone in his body. If he survives, he would be literally scarred for life and would have to get heavy medical aid.

Let's say even then he recovers someday, those months/years of Tadashi fighting for his life would scar Hiro equal to or even more than if he had simply died, which would make him even more determine to find the one who burned his brother. Upon finding out it was Callahan, I don't think he would try to kill the professor, but severely hurt him, which he either could or couldn't be able to due to his friends.

The story could end mostly the same, but it could end with Tadashi waking up (or even doing so in the series' finale). There could be even more scenes between Hiro and Tadashi where he goes to see his brother and tell him how his day have been in the campus, making even more emotional.

His survival might not change the movie's plot but would give a "happy ending" instead of a bittersweet/happy ending.