Sergio Marchionne is one amazing guy. First, he takes over the old Fix It Again Tony car company and straightens it out in record time. Then they give him a basket case called Chrysler and he pulls another rabbit out of his hat.

Unlike other top executives who regale in the pomp and circumstance their heady status affords them, Marchionne likes to saunter into meetings wearing his trademark sweater and backpack and disarmingly casual style. But don’t let this “I’m-just-an easy-going-guy” persona fool you, especially if you work for him. It’s the last mistake you’ll ever make.

As I see it, there are two secrets to his success. First, he knows how to cut through complexity and clearly prioritize what needs to be done. Second, he has a knack for finding fresh talent within an organization and giving them mountains of responsibility.

The top executives in Marchionne’s organization get two jobs. That’s his way of forcing them to delegate. After all, there’s no way they can do two completely separate jobs. Not full-time, that is. They have to delegate.

Marchionne loves a flat corporate organization. Whereas other CEO’s embrace the traditional pyramid-shaped organization with them at the top and seven or eight vice presidents reporting to them, he has something like 36 direct reports.

Marchionne likes to move fast and a flat organization enables that. Of course that means he has to be involved in all parts of the business all the time. I don’t know of any other executive who could make this kind of organization work. I wonder if his board does.

How does he do it? Marchionne is the consummate workaholic. If he’s not asleep he’s working. And he doesn’t sleep much. He uses six BlackBerry smartphones to keep in constant communication with the different parts of the Fiat-Chrysler empire he oversees. It’s a Herculean effort. And therein lies the Achilles’ Heel in his system.

What if, God forbid, Marchionne steps off a curb tomorrow and gets hit by a bus? Who could replace him? Or better stated, what other CEO could possibly work with his flat organization and 36 direct reports? I don’t think there’s anybody out there who could or would.

That means the Fiat-Chrysler boards better be worrying about more than their succession plan. They also should be thinking about a complete organizational change when the day comes.

But for now, all the boards can do is worry. What else are they going to do? They can’t argue with Marchionne’s success, and they certainly don’t want to slow the guy down. All they can do is pray he stays healthy and happy.

Chrysler is a company that has gone through tremendous turmoil in the last decade. Daimler ran it one way; Cerberus ran it another. Neither ran it well. In fact, it’s amazing Chrysler has survived. Now Marchionne is running it in a completely new way, and that seems to be working.

Maybe one of his direct reports could step in when Marchionne steps down. But my guess is Chrysler is facing yet another massive organizational change before the decade is out.

John McElroy is editorial director of Blue Sky Productions and producer of “Autoline” for WTVS-Channel 56, Detroit, and “Autoline Daily,” the online video newscast.