This has essentially happened already. Comedy central censors South Park in a direct response to threats made against them regarding depictions of Mohammed.
Incidentally this episode aired nine years earlier with no controversy over showing Mohammed. Though after 201 aired they did take down Super Best Friends.
Seth Rogen is a bit of a coward. He picked an easy target in Kim given that North Korea is isolated and has no ability to do any real harm to him. Easy to mock somebody who can't get back at you.
Would he have dared to make a comedy mocking Mohammed the warlord turned prophet and 72 virgins in heaven? I guess he was smart enough to figure out that life under police protection would have cramped his partying.
Oh, and Seth is a total prima-donna, witness his recent tirade against Cathay Pacific because they wouldn't allow his wife's dog onto the plane due to the breed being more susceptible to death during flight.
That "ancient religious figure" is arguably causing real harm to real people right now, too. If anything, the difference should be that mocking "ancient religious figure" should be risk-free, while mocking psychos with nuclear weapons is rather risky. How it became exactly the opposite is beyond me.