There is a technology to cleaning floors that has been used since the 1930's to maintain hardwood floors that can be equally well used for marble floors. In a nutshell, that technology calls for the homeowner to cover the floor with a sacrificial coating of some sort (think "floor wax") that can be renewed periodically to restore the floor to it's original condition. That is, shoe leather never touches the marble cuz there's always a layer of something between the two that wears out instead.
Nowadays, that layer would typically consist of two or three coats of acrylic sealer and 5 to 8 coats of acrylic floor finish. The sealers is meant to be permanent, and it's job is to protect the floor from stains. The finish is what wears down, and it can be repaired or replaced to restore the appearance of the floor. This is what's done on vinyl composition tile floors, which is why vinyl composition tile floors are most often used in commercial settings... the finish on them can be maintained to look like a new for the entire life of the building they're installed in. Since it's only the acrylic floor finish that takes the wear, and this finish is continually repaired or replaced, the underlying flooring essentially lasts indefinitely. It's like asking how long a floor would last if you keep replacing the carpet on it. The answer would be "indefinitely".
Nowadays, no one uses floor wax anymore. It's way too soft, and so it doesn't last long without becoming all scratched and damaged and looking dull in the traffic areas. What people use nowadays are acrylic sealers and acrylic floor finishes which have higher gloss and are harder than Carnauba Wax (real floor wax). Acrylic floor finishes stay glossy longer than floor wax ever did, and so they require much less maintenance. I use an acrylic floor finish called Carefree (made by the S. C. Johnson Wax Company) on each of the apartments in my building.
Basically, you CAN strip all the acrylic floor finish off your floor and replace it to restore the appearance of the floor, but the more practical solution is just to use a floor machine like this one:
to scrub off the dirty, rough and damaged surface of the acrylic floor finish, and then mop down new floor finish to replace what was scrubbed off.
The problem is that a floor machine like the one pictured above will cost about $2000 brand new, but you can get smaller and more basic models for $1000. Generally, there aren't too many used floor machines on the market, but if you can find a used floor machine in good condition, that would be another option.
Eurostone Marble Inc.com
Without doing the above, about the only way to keep a marble floor looking new would be to keep polishing down the roughened surface of the marble.