there isn't going to be any load on the pinion, it'll be perfectly fine. my rear end blew up last year(sheared 3 pinion teeth 
) and i drove it around in front wheel drive. it definitely didn't make the noise that it was making when i had the rear driveshaft attached.
But the pinion and pinion bearings will still be rotating with uot the proper preload on them. this will subjuect the bearings to improper wear and could over heat them or make the pinion start to walk in or out. This is worse case scenario and it's not my ride so what the hell put her to the wood tell the vavles float and side step the clutch tell you start rolling smoke
