So, after a lot of thinking I finally got a clonclusion of why did Goku go with Shenron, why did he appear and disappear so quickly when he was with Krillin and all that stuff.
As the story tells, the Dragon Balls couldn't be used anymore because of the negative energy within them. So Goku decided to give his positive energy to make the Dragon Balls work one more time, giving his life. But then he absorbed them, becoming a god-like thing, so he could keep his body and still interact with people, but I'm guessing it wasn't allowed to a god interact with mortals, anyway Shenron let him visit his friends before leaving with Shenron. I'm thinking that Master Roshi knew he was dead and also Vegeta because they couldn't sense his ki. Krillin and the others were not that used to fighting, so that's why they didn't notice.
So he comes back 100 years after, to watch the World Tournament, as he used to do before.
This may be the answer, but I think the ending of Dragon Ball GT was made on purpose to make the spectator imagine its own finale, like Goku coming back or something.
As the story tells, the Dragon Balls couldn't be used anymore because of the negative energy within them. So Goku decided to give his positive energy to make the Dragon Balls work one more time, giving his life. But then he absorbed them, becoming a god-like thing, so he could keep his body and still interact with people, but I'm guessing it wasn't allowed to a god interact with mortals, anyway Shenron let him visit his friends before leaving with Shenron. I'm thinking that Master Roshi knew he was dead and also Vegeta because they couldn't sense his ki. Krillin and the others were not that used to fighting, so that's why they didn't notice.
So he comes back 100 years after, to watch the World Tournament, as he used to do before.
This may be the answer, but I think the ending of Dragon Ball GT was made on purpose to make the spectator imagine its own finale, like Goku coming back or something.