Responses
i think what happened is that she gave all her Alice power(the 3 of them) to Natsume, and the Alice users with the same syndrome as him or his mother normaly die because they have NO MORE Alice power left in them. So now he wont die young as long as he doesnt overuse his power as he did before. Also, even if i find it a bit confusing, the Natsume from the past/present IS in fact the same Natsume. So he did recieved the power of Mikan, died AND also did not died. That's also the reason why Hotaru and her brother had to pay the price of playing with space rules :/
You know when they take Natsume to the past, trying to save him...
Well they replace the breathing one with the dead one, so the future should have been changed ; Mikan couldn't have used all her Alice on him since he was already dead...
Also, the fact that she ends up loosing her Alice... well, she has 3 alices so the only one she could have lost was the "inserting stone" alice or maybe the "stealing alice", but her nullification would still be there, right ?
I think it's so cruel that they made her leave the academy and even erased her memories, she was so happy with everyone ! And Natsume can't live for long because of his life shortening alice, so they missed 4years together.... and she couldn't stay with Ruka-Pyon neither (Rukaaa <3).....