The same way people can't accept a Batman without a Bruce Wayne, though there have been episodes but wo baat nahi hai .
Who knows about the Joker! May be Tony Stark is more crazier than the Joker. The Joker might be tempted too much by the partying and all & finally Iron Man will bring him down .
Uhh... The Dick Grayson Batman and Terry McGinnis Batman are accepted as real Batmen. The Batman Inc Batmen are accepted as real batmen.
Tony Stark is definitely not crazier than the Joker. He has been analyzed and exploited by SHIELD multiple times. If the Joker is tempted by the party he will take over it or go in and prank everyone. Considering how loose Tony Stark is after having a little alcohol and how none of his parties are without alcohol, there is no way he would be able to take the Joker down.