Tony Starks wealth, his charisma, his untold amounts of girlfriends, as well as his vast industrial resources not only make him a focal point for the heroes of the MCU to gather around, but also an indispensable one. Stark has it all: economic resources to provide for vital materiel for the heroes needs; he can bankroll a headquarters, obtain any piece of technology in the world and even liaison with the government to provide necessary intelligence to the heroes. As Iron Man, he has super-powers as well as his own fan-base. In short, Iron Man is a golden character who can either act on his own initiative or be a part of the bigger whole. Iron Man is a superstar. Of course, this shouldnt come as a surprise to the thousands of Iron Man comic fans. This is Starks role in the comics. Its a natural extension of the Iron Man character that these fans have grown up reading since the late sixties and a role that all will expect for the cinematic version. But Iron Man is a character that the Avengers cannot do without. With SHIELDs dismantling and disavowed nature, only Tony Stark has the resources and influence to be able to fund a similar organization, or to provide logistical support to a new group of super-heroes like the Avengers in their absence. Stark fits into the MCU as an axiomatic figurehead; removing him would be like removing the axle from a wheel.