Yes, Goku practically became Shenron, that's why when he was riding on him at the end of GT the dragon balls sort of went inside him and that's how he appeared when Goku jr. was trying to use the dragon balls.
GT never existed in the Dragon Ball unierse since Toriyama (original creator of Dragon Ball) stated that GT was non-canon,I'm just saying this everywhere.It is true though,look it up if you want to.Some argue that it was just a rumor though,so we may never know..GT was completely horrible in my opinion
Goku had went to train because Vegeta had asked him (Goku) if he was going to train and Goku said to shhhh. That is what happened to Goku, he went to train.
You may thank me later ( joke)(I know its not funny).
Well he didn't really die, but no one exactly knows what happened after that point. He could have survived until the final part of GT at the World Tournament, he could have traveled to different places training with Shenron, he could have died. No one know for sure