The moon has large enough density variations that you can't analyze low orbits as though it's just a point mass.

Yes, I know about the masscons, but it seems highly unlikely they'll be just at the right point. It's hard to believe that any object given a single impulse at ground level, in a vacuum, is not going to hit the moon again in one orbit (unless it is given escape velocity).

Masscons did perturb the Apollo missions enough that they had to switch to a doppler radio to navigate accurately.

Don't forget electric fields are involved too on Moon. They are strong enough to levitate the dust sometimes.

The paper models an 'ejecta sheet' of particles that exceed the escape velocity of the moon and thus aren't in orbit.

If they achieve escape velocity, then they won't be hanging around the moon.

Sure, the article doesn't say that something would be hanging around the moon permanently, it evaluates the damage that might occur if the orbiting spacecraft passes through the splash of debris ('the ejecta sheet') as it's happening - it doesn't really attempt to evaluate how likely it is to hit it, the discussion is about the expected consequences if it happens.

Although it does assert that the NASA Gateway orbit passing through the ejecta sheet "will probably be several times before the sheet is dispersed."

Yes, that's why I said "only in the immediate aftermath of a landing".

The problem is, your orbiter is necessarily in orbit at the same time that your lander is making its landing. And the lander kicks up debris that can then threaten the orbiter.

Is it going to get into an orbit? I'm guessing it's only in the immediate aftermath of a landing. I think you misinterpreted my comment.