They want to move it to L2, it's not going to be anywhere near the earth to bother with.
If the thruster runs too long, it'll overshoot L2, and go into an orbit rather far out of the moon's orbit.
Chance it crashes on the moon is rather higher than it crashing on earth, and even then it'll not be an overly significant event (see someone else's calculations in this reply thread as well)
L2 is perfect for this stuff, since it's actually outside the earth's sun orbit and farther away than the moon.
Now L3,4,5 which are located on the earth trajectory might be something you might not want to do :) (If I remember the locations correctly..)