In theory yes but there a a few unknown factors to consider. 1. Is there a limit to guardians lifespan - we don't know if a ghost can resurrect endlessly or if ghosts battery lasts forever as that ceiling could just be extremely high. Bare in mind guardians are roughly 1 to 1000 years old can't give an accurate guess as the lore is unclear on the time and dates of stuff like the collapse and founding of the iron Lords or battle of twilight gap. So determining if guardians is truly immortal is impossible without date and more time. 2. The witness what a million plus years plus the history and accumulated knowledge of and entire race that was deeply knowledgeable of the light and darkness. 3. Would your ghost betray you and stand against. 4. Can the traveller stop you as you start your move - if ghost is connected to the traveller and we gain the light through ghost than could the traveller cut the connection.

Well Darkness power was only part of it. You need control of Light to reshape reality. The whole Witness thing was drummed up last minute. Heck they even admitted there wasn’t any real Darkness to begin with when D2 dropped. That’s why there’s no hint of him ever in the lore until he just shows up. The whole end game was a retcon. Which is why it’s weirdly convoluted and silly.