For years people shifted non-synchro crash boxed on the move double clutching all over the place. a lot of light grinding happened here and there and those transmissions just kept going.
I was in the Philippines a few years back and our hired driver had a synchro out on one gear. In a 45 mile drive with hundreds of gear shifts I heard him grind it lightly several times. I asked how long the synchronizer has been out. He said about 100,000 kilometers - don't know if that tells you anything.
All that said, jam the lever in hard when it doesn't want to go and you can break something. If he just started the PTO with no load (no attachment) and incomplete clutch disengagement it probably didn't do any harm. If you had something hooked to the PTO might be a different story.