Goku's power is based on KI, body energy. What he does is manipulating and concetraiting that power in projectiles. Galactus can easily get him away of concetrating that power (that case he dies coz then his life essence is gone too). And note that Goku dies in space. He is still human. Galactus could just whipe the floor with Goku.
He won't be able to that. He can't. He is a KI based character. Like I said he need to concetrate his power to do something. He can't teleport inside Galactus. In that he would have killed Cell in seconds. Or Bebi. And when he was fighting Bebi he was SSJ4....So I doubt that. Ka-Me-Ha-Me-Ha that takes him 3-4 seconds to say. Galactus just makes him a piece of pizza in that time. And even if Goku could do his stuff that won't do any demage. Coz it's only projectile manifestation of his energy.