I don't know if this theory is mine or someone else's. So don't sue me or something.
So Thomas Astruc tweeted that Chat Noir will die at the end of season 4. :'( I don't know how, but I think it's because Ladybug gets akumatized. There was a leak in the names of the episodes (I don't know if they're fake or not) and the last episode is called Lady Misfortune. We, as crazy fans, know that Lady Misfortune is the name of Ladybug akumatized. So maybe Chat dies as a result of her getting akumatized.
What do you think about this? The review box is waiting for your answer!