Helicopter pilot leaving cockpit  

Every HEMS/HAA operator I worked for had an SOP in place for the pilot to leave the cockpit with the rotors turning if necessary.  Usually on a scene call when there wasn't security available for the aircraft, typically to guard the tail rotor.

As long as the aircraft is at idle, with the collective locked down and the cyclic frictioned in a level attitude, it isn't too big a risk.  The only advise I'd offer is:

Only do it if absolutely neccessary, and refueling usually isn't one of those times.

Be absolutely sure the collective lock is fuctioning properly!  They have been know to get worn and not work well.  That could be a disaster, even at idle!

Be sure to release the cyclic friction prior to trying to take off.  (Unfortunately, the voice of experience talking)