Believe it or not but this almost exact plot was done in an episode of The Night Gallery back in 1969. In "The escape route" a fugitive nazi somehow transfers his soul into a painting of a man fishing, except in the end when he finally transfers his soul all the way he goes into the wrong painting, etc, etc.
I think the implication (for The Unfunnies) for how he can escape into that world is that because he put his own heart and soul into making it he has a supernatural connection to that universe. >He basically just locked himself into his own personal hell. It doesn't matter if he says he's looking forward to doing terrible shit, because before the year is out he's gonna be bored and by the end of the decade he'll have killed himself.
Debatable, especially considering he mentions that there is nothing after you die. If we take the story at his word and accept that he really did magic himself into that world then he really might be happy simply torturing the inhabitants of his cartoon world for eternity or however long that universe lasts. It could be that the "Funnies" universe only exists so long as media and/or memories of it exist in our world. In which case he only prolonged the inevitable.>>118689605
I like your take on it too, that he's just having a mental breakdown and reliving his life from the perspectives of his characters in his own nightmare world. A nightmare that will soon be ending when he is executed.