I've done one 'in anger' windmill start successfully, and if memory serves me right, the manual said you had to give it away with 5000' of runway remaining, (which was very conservative). I know a bloke who managed to get the last engine of an 'E' model up and running after a starter failure at Nui Dat, in South Vietnam - which was only 5,000' long. I suspect the latter stages of that windmill start that would have been a tad exciting, if not for the crew, then certainly for the grunts at the end of the field.
He got a king size kick in the arse on getting home, but the chances of the Herc ending up as a smoking pile of burnt aluminium had he stayed at Nui Dat overnight were pretty high. (They didn't call the silvers Hercs 'mortar magnets' without good reason.) And he got the load of very badly wounded medevac cases out to Butterworth that day.
The buddy start, where the aircraft with the dead starter lined up behind another Herc who then ran his engines at takeoff power was in the manual, but highly discouraged because of damage the aircraft at the rear would almost certainly suffer from stones and all manner of other junk kicked up by the propwash of the aircraft in front.