Like I said everyone misses the point , ITS MULTIPLAYER not single player, so even if one player cannot see it server still need to keep track of it
The things that exist on the server are different than the things that exist on the client.
There is nothing preventing you from using fixed point math in one representation --- as discussed with the world as a fixed point 64-bit integer --- and also having a floating point representation used for your client game engine.
The most common practice that I read about for overcoming floating point precision in video games with large worlds is by dividing the world into cells and load it with player's position and shift origin of objects with respect to player.
Note that this is extremely common because it is very effective.
Floating point works well for most games, assuming a meter scale, up to about a 4 km value from center. That's +/- 4km in x and in y, or about 64 square kilometers, or about 25 square miles. That's an enormous area.
Occasionally, perhaps after you've traveled a kilometer or two, or a mile or so, you update the world so you're in a new center location.
Even for large worlds it is rare for RPG-style games to cover more distance than that in a single region. WoW is currently on the order of 60 square miles of actual content. Most of the older areas are vacant ghost-towns. Skyrim and Dragon Age Inquisition are both on the order of 20 square miles of content. GTA 5 covered about 100 square miles, but the vast majority of it was fake/duplicate buildings. It was probably around 2-3 square miles of actual modeled stuff plus about 10 miles of modeled roadway segments.