I was bending a pawpaw branch to see if i could train it to grow horizontally and it just peeled off with some bark. This is how it looks a couple weeks later. 20190728_200047|690x517
Your leader will be fine. I would saw off the dead stub flush with the leader then take a very sharp knife and cut a sharp, clean edge on the wound. Cut away dead material (brown) and cut back into green, live wood. Smooth, straight edge heals quickly; ragged, jagged wounds heal slowly or never do quite heal.
i wouldn’t worry about the tree he will be okay. why do you want to train him? don’t most pawpaw grafts die after ~12 years? pawpaw i think i would let grow more wild or bushy form than any other fruit tree.
I hope it lasts longer than 12 years. I planted it in 2016 and finally took off this year. It was chest high in Spring and now it’s close to 7 ft tall. Hopefully I get some fruit next year.