I'd say it depends on if your engineering talent is vastly superior today than what it was when it was written. Even then it's so risky. It's probably always better to do it incrementally even if it takes twice as long to do so, because you can maintain working software and fix bugs as you go.
The approach I would take is to get the minimum set of engineers who know the most about each major aspect of the code, and put their heads together on what the ideal architecture would be. But rather than building it from scratch, figure out how to implement just one of those pieces now. That way you can decrease entropy in the codebase piecemeal without chucking out all the code at once, which is no doubt full of forgotten assumptions that no one will remember until it's too late.
The approach I would take is to get the minimum set of engineers who know the most about each major aspect of the code, and put their heads together on what the ideal architecture would be. But rather than building it from scratch, figure out how to implement just one of those pieces now. That way you can decrease entropy in the codebase piecemeal without chucking out all the code at once, which is no doubt full of forgotten assumptions that no one will remember until it's too late.