The Adeptus Custodes never leave Terra and rarely if ever leave the Imperial Palace. Would they seek to maintain the personal battle barge of the Emperor in the event he is ever healed or reborn?
Also how would the Adeptus Custodes be portrayed in the game? Since they are above and beyond even the Astartes as capable warriors. One thousand of them routed and destroyed one hundred thousand orks and they lost only 3 custodians. So that speaks volumes of their skill and equipment.