I think that I may be not the only one that has a gut feeling on the fact that maybe Isayama may pull a Fairy Tail card on us where by some unexplained occurrence causes the curse to be lifted right before our Suicidal Bastard dies, ending the series with a fairly cliche tone as Eren and Mikasa get together (Not that I mind.) and so do the others. If that were to happen, SNK would no longer be a unique Shounen series since it followed the same road as other big series.
why i think so:-
1) Keith Shadis said Grisha Yeager came to walls 15 years before the attack on shiganshina.
this means that grisha Yeager from the time of his arrival to the time of his death, lived 15 years, more than 13, which defies the curse. could it be that he found a cure?
2) Even so, the shifters body wears out during 12th year just like uri’s body did, even though he was young. Grisha looked fine which means that he was ok at the time he was devoured by eren, which was around the 14th year after him getting the shifter power. it could be that he cured himself of his ailments.