I aksed my equine dentist that question when I foudn out Zar had a cracked molar. Well i asked about removing it. He said to leave it unless it abcesses or gets loose, because even cracked it will help him digest his food more (by grinding it up before it hits his stomach). The fewer teeth a horse has the harder he is to keep. I dont rememebr any answer to the abcess. But Zar has lived it with just fine for years. This past winter has been the only time he has seemed to be having problems with his weight (he is 20 and a once abused, rescued, then sent to slaughter, then rescued again horse). So when I get my ED out again will have him check out that tooth. Will have my vet out before so will see what he says.
I do know that my ED said that a horse does not have nerves IN the tooth which is why they can cut them off, saw them down et. And its the nerve (at least in humans, lost so many teeth that way.. mine crack eating bread..
) that will get infected. So as long as she isnt cutting her gums giving an opening for an infection there to start... I would think there isnt much you can do to prevent an infection.
As far as selling, just make the new owners aware of the situation and make sure they understand it. Never noticed that a hard keeper is harder place then an easy keeper. but who knows??