Do you know yet if he got the job or do you just assume he will? If he doesn't have it yet, you have to force it out of your mind so you don't waste your precious time worrying about something you can't control. If he does get it, you'll probably do better than you think. Maybe when you hear his voice you won't "see" him. Focus on the work, not the person. Sounds like you have moved on anyway, it probably won't be as bad as you fear. My stbx still lives in my house, we haven't spoken in over a month until yesterday. I was putting out the trash (this used to be his job, but a couple of weeks ago he came home too late/drunk to remember to put it out...I go to work early and get the kids to school so he usually takes care of this). Anyway, so I added this onto the list of basically everything else I do. I was putting it out and 'he' came out. I just looked at him and said "I got the trash". He has to be controlling and glare and me and say "I" (emphasis on "I") "got the trash". I thought, why do you have to be such an a$$hole, but instead I just went inside and got ready for work. Anyway, point I am trying to make is when I saw his face, heard his voice (as I said, been over a month) I really didn't get the usual emotions attached to that. He looked like any guy on the street. You are so much further along in the process than me, so maybe when you hear his voice you won't associate it with the memories, it'll just be another male voice in a conference call.
Anyway, try not to worry about it now, and if he does get the job, have faith that you will handle it fine. I am glad you are not considering quitting because of him, I would guess he'd just LOVE to know he could cause that! Keep the love of your family close to your heart, your ex can't get to you anymore.
Very interesting question. My ex and I have worked at the same company for almost 10 years. He started there before I did and I have no involvement with his side of things, because I work for one of the partners and he works for the big boss. It hasn't been a big deal for us, simply because of that small fact. :)