Ashley, I am so sorry to hear of your Dad's passing. He was very young to have this happen and that just breaks my heart when people pass so young...
I have to tell you that you did the right thing spending that time with him and you are right, you did not have to stay till the last breath. I thought when my Mom passed it would be relief for me to be there for that last breath and know she was not in pain anymore, but it was not... As far as him knowing you were there, I believe he knew....even though not conscious, I think somehow they know...
Please know that I am keeping you in my prayers as you go through the next few days and the days after that......Hugs and do check in with us and let us know how you are doing...
Again, I am so sorry about your Dad.