The deployment of 100MT of SBSP (25 TW) using LOX/LH rockets could result in as much as 40 MT of plume molecules in retrograde orbits.
Other "rockets" might use electrically superheated hydrogen, or ion engines (though there is not nearly enough xenon and krypton for that). Laser ablation thrusters are possible, but those make a dog's breakfast of hot, poorly collimated molecules and ions compared to "clean" hydrogen-based thrust.
Let's focus on LOX/LH chemical engines with an oxidizer:fuel mass ratio of 5:1, resulting in a 15:1 mass ratio of H₂O and H₂ plume molecules. For 40 MT of plume, that is 1.67e36 H₂0 molecules, and 1e36 H₂ molecules. They will be emitted over years, but many may persist.
5 O(16) + 8 H₂ -> 5 H₂O + 3 H₂ = 90 AMU of H₂O and 6 AMU of H₂
The collision cross section of H₂0 is 15.5e-20 m² and the collision cross section of H₂ is 5.75e-20 m², so the total collision cross section of the entire plume is 2.6e17 + 0.58e17 m² = 3.16e17m² = 3.16e11 km², equivalent to a spherical shell 160,000 km in diameter. The atoms are in elliptical orbits, with a starting apogee at GEO; they will frequently collide with each other and spread into a rotating cloud.
MoreLater, including guestimate of how the atoms will scatter downwards into the atmosphere, and outwards to escape, but mostly form into a swirling donut of retrograde gas molecules and atoms with approximately the same (WAG) angular momentum and a sizeable fraction of the mass of the original plume constellation.