And another aspect is that, if nobody ever knew he was Spider-man, that means Tony Stark never knew he was Spider-man. Technically he should lose the fancy suits and gadgets the moment the spell completes.
If he loses the gadgets, then he probably dies at the hands of Mysterio, and isn't able to ask for the spell to be cast - paradox.
Luckily, Tony is dead. It is like he's hiding in an apocalypse - the information didn't and can't leak from him, so he can know... and then die again, and everything's fine.