Galactus comes to devour these worlds, what happens
These guys use there standard defences and technology to defend them selves and any heroes there
1. Krypton before destruction
2. Krypton under yellow sun
3. Asgard
4. Mars before the Manhunters were wiped out
5. Apokolips
6. New Genesis
7. Shiar Homeworld
Assuming the inhabitants are there, trying to stop him, Galactus gets stopped every time. The fundamental role of the "devourer" Galactus was to be weak enough (while hungry) to not pose a threat to advanced, worthy civilizations. Instead, he weeded out the weak. He never managed to devour the Earth, he's not going to devour any of the planets mentioned in the OP, either.
Galactus...
1. gets sent to the Phantom Zone.
2. gets utterly stomped by a planetful of Supermen lol.
3. gets stopped by an amped, Odin-inhabited Destroyer.
4. gets taken out by the combined forces of green and white martians (but manages to take out J'onn in the process).
5. gets enslaved by Darkseid.
6. gets boomtubed.
7. gets erased by an Eleka'an event horizon.
G fails in every case.
Re: Galactus comes to devour these worlds, what happens
1. Krypton before destruction. Galactus gets a new Herald. Jor-El.
2. Krypton under yellow sun. Galactus gets a new Herald. Zod.
3. Asgard. Galactus gets a new Herald. Sif.
4. Mars before the Manhunters were wiped out. Galactus gets a new Herald. Not J'onn.
5. Apokolips. Galactus gets a new Herald. Mr. Miracle.
6. New Genesis. Galactus gets a new Herald. Orion.
7. Shiar Homeworld. Galactus gets a new Herald. Gladiator.