That's too bad. I think it's pretty bullshit. It's like offering to buy a nice-looking car for the price of a cherry example only to find out its floor is rusted out and the engine is locked up before money has actually changed hands, but the slimy salesman has managed to convince the law that the buyers should be forced to buy it anyway, and at the inflated price.
In this case, Musk absolutely screwed himself over by explicitly waiving due diligence because he wanted the most expedited possible sale. He really cannot then turn around and argue that the sale contract should be voided on the basis of alleged fact finding, because that's literally what due diligence is and he already voluntarily waived that.
To use your car example, this is like someone not only choosing to sign a "purchased as-is" contract for a used car without having a mechanic look at it, but proactively suggesting a waiver of all implied warranty because they don't want to "waste time".
In other words: Musk actively chose to be insanely reckless in his hasty purchase offer, then started crying about "no take backs".