There have been many posts about Tadashi Hamada ( Hiro's Big Bro ), not dying during the fire in [Big Hero 6](movie:425271) . If that were the Case ( because of not finding his body), where is Tadashi now?
Remember This Island?
Yeah. This Island...Akuma Island. Where Hiro and the gang found out about the new Teleportion experiment that krei tech were doing, and where baymax located the Mask Man, later to have be callaghan. If this island was able to hide callaghan from the rest of San Fransokyo, maybe Tadashi could be there too. Its a big enough island; alot of hiding spots could be found.
And Lets Not Forget...
If the Theory of Tadashi being Sunrise and having to be the villian, ( If Big Hero 7 is made)... Wouldnt he need somewhere to hide; Just like callaghan. If so Akuma Island would be the first place to look wouldnt it. And it would be most likely that the rise of Sunfire had happened at the university during the showcase, as there were so many scientific tech and creations there. There must have been atleast one of them that had cause a reaction on Tadashi and created that mass explosion seconds after he went in after Callaghan.
Baymax... Does he know?
Baymax was created by Tadashi. Near the end we see that when Tadashi finally got baymax to work, he scanned him. when baymax scans people he finds information and can find them when needed. But we didnt know that he scanned Tadashi till the reply of Tadashi's tests shown by Baymax. Keeping that in mind, the second time when Hiro meets Baymax, he tells him " Tadashi is gone... he isnt coming back." Baymax replies with " But he is still here." However Hiro took that as emotion help, to get his mood together. However, Baymax himself said that he was made for emotion pain ,but physical, and downloaded emotion help to his drive only after he said Tadashi was still there. When they went to the harbour. What if after Hiro told him about Tadashi, Baymax scanned from him. It would make the most sense as Baymax can do that or maybe he just knows.... Robot's intuition?