The whole sentence is "He drained the medallion company of all the cash he could and lit out for Israel, leaving his company as a shell in the rearview mirror." I've already searched and understood what a shell of a rearview mirror is. But I cannot find the connection of it to the "leaving" part.
They are two separate thoughts, the company is left "as a shell", in other words it has been hollowed out by draining it of cash.
When you leave something behind you can, perhaps, see it in your rearview mirror of your car.
Of course the man in question didn't head to Israel from the USA in a car, so it's a metaphor. And, as Robusto points out, so is the "shell" so it's a mixed metaphor.
This particular one combines two reasonably compatible metaphors, but mixed metaphors can be absurd.
In accounting and finance, "shell" is a technical term, not a metaphor or jargon. It refers to a corporation that has no assets, not even stock in another corporation. This company seems to own a taxi medallion. This is a valuable asset, but it can't be seized by creditors, so the company is a "shell" from their point of view.