Without a living Hitler, the odds of Valkyrie being successful go up, as IIRC the whole point was to pin his death on those best able to seize control of the state and then unleash the Army on them. It was the revelation Hitler was still alive that caused the coup to unravel.
However, if Himmler and company are able to escape the initial coup somehow, they might be able to rally resistance to Von Stauffenberg and company.