I think what is going to happen is someone will make a big sacrifice or a miracle will happen.
If Karasuma really dies at the end, I cant really see Karasuma dying here, maybe in a state of coma, by the way I read in other chapters the translation of 261 and it seems like really big one... I think one of these 3 things happened:
Karasuma rejected tenma because of his illness... Karasuma told Tenma the truth... or its a big misunderstanding.

