With the latest chapter of My Hero Academia's manga, the past of One For All has been explored, with Deku having a tete-a-tete with the predecessors of the Quirk that was passed on from All Might to Midoriya. With more mysteries unveiled with regards to One For All, it seems as if this is definitely a case of "ignorance is bliss" as Deku learns that the powerful Quirk might not be passed off once his time has come to an end.
Warning: My Hero Academia chapter 304 SPOILERS Follow!
The aftermath of My Hero Academia's War arc has seen the heroes defeated, even in their victory over the League of Villains' army. Dabi's psychological blow from revealing his connection to Endeavor (and Hawks' criminal origins) has crumbled pro hero society with public distrust and hero retirements. Endeavor, Hawks, Izuku and Bakugo are all still seriously injured, with Izuku left comatose after All For One tried to siphon OFA from him in battle.
As stated, the interior story of Izuku's journey through the realm of OFA is very different than anything we've seen before. Izuku finds himself in a room with the One For All predecessors, instead of the empty void he typically experiences. Deku also figures out how to speak directly with the predecessors.
OFA's predecessors have brought Deku in for an important history lesson, regarding the life (and death) of OFA's 4th user, Hikage Shinomori. Turns out Hikage was a recluse who tried to spend his life training and building up One For All, instead of using it as a hero. However, Shinomori ended up dying of "old age" when he was only 40, revealing a key detail about One For All: it's too much power for someone that already has a quirk. Shinomori's death is proof that One For All's true power can only be held by someone who is quirkless.
Therein lies the game-changing rub of My Hero Academia's biggest hero power. All Might became a "true holder" of One For All since he was quirkless, and it was a small miracle he found Izuku Midoriya, another quirkless person to pass it onto. As One For All's original user tells Izuku, the odds of him finding another quirkless person of this generation, who truly needs the power of OFA, are slim to none. Deku can't give it to a person with a quirk, and will likely have no option to pass it onto a worthy quirkless user, either.
In other words: My Hero Academia has established that One For All can no longer be passed on, and Izuku Midoriya is likely its final user. So if he falls, the only power that can stop All For One apparently goes with him.