I'm talking about GT. Trunks was already born. He was like 17. If he went back in time, Goku would just follow Inuyuasha and throw him into a black hole. Nobody can save him or bring him back to life then. If Kagome was searching for the Dragonballs to bring him back to life, Goku would stop her. If your thinking since nothing not even the speed of light can escape a black hole, which is true! Not even light can escape a black hole. So Goku would use his instant transmission technique to teleport and get out of there. He's faster then light at ss4 but just to be safe he'll teleport.