Leftover fuel should be enough to get back to the overworld. Make sure you bring an empty liquid canister though, the fuel is stored in the lander.
Keep in mind you don't have to use the Galacticraft provided by the mod pack, (as long as your in 1.6.2), you can always update your galacticraft manually to get Mars.
Keep in mind you don't have to use the Galacticraft provided by the mod pack, (as long as your in 1.6.2), you can always update your galacticraft manually to get Mars.