I have lost but a few in my lifetime and they haunt you for a very long time afterwards.
You did a great and nobel thing by tracking that buck down and finishing the job, but the way you described the wound he may have survived had you not found him. It's always better to be sure and finish the job with whatever it takes to get er done!
I hit a doe in the shoulder one season and knocked her flat to the ground, broke the shoulder and somehow missed the vitals. My brother and I tracked that doe for over a mile until the blood trail completely quit and she never laid down, not once.
The next year I saw her with twin fawns and how I know it was her was the hump she had in the top of her shoulder when she walked. The shoulder blade grew back a bit out of place and it produced a little hump under the skin when whe walked......we nick named her "Humpy"
Long story short......Humpy went on to live another 5 years raising twins every year until my uncle shot her during gun season one year. She didn't have any fawns that year and she was dry....no milk bag. Even though she survived a broken shoulder and a broadhead through the brisket she healed up just fine and got around just great like it never happened and raised fawns every year until she became barren, and ended up living an otherwise normal life.
I know that still doesn't make it right by any means, but sometimes there is a happy ending to a horror story........every once in awhile.