All of mine have done just fine. We never started with overnights, though, just left one behind when we went riding, then for a weekend, and later for 4-5 days. They will call occasionally, but nobody has gotten scarily agitated or hurt. As long as your fencing and footing are safe, I wouldn't worry excessively. A dry run is a good idea, but don't give up if she is upset 15 minutes in.
I am sure I have driven my husband crazy, calling to ask how the left behind horse is doing. "Still on four legs" is his answer. Sometimes, they don't even get excited when we return.
Different situation. How would yours behave if you took their herd away from them, rather than taking them away from their herd?
I know 4 that would be fine.
3 have had rest of barn taken to 4 day/week long shows. Each had been left alone on separate occasions.
1 stayed @ farm when hurricane came through & flooded stalls on back wall-rest moved to another facility for a week.
I have 2 horses at home and take my gelding away every so often for shows and trail rides leaving my mare alone. He has also been hospitalized twice so he was away for almost 2 weeks once and another week on a separate time. She usually starts out kind of frantic and upset, but settles in. I started locking her in her stall when he first leaves because she will otherwise pace the fence and quiets down faster in her stall. She has gotten very anxious about being locked in now but overall is much better and settles faster when he is gone. Usually by the time i get back her hay is gone and she is quiet and actually doesn't even notice us coming down the driveway. When he was gone for longer periods of time she seemed a bit depressed but she did okay. I felt bad for her though. I tried borrowing a pony and would bring him over when i would take my mare but she honestly had no interest in the pony and he stress level /pacing didn't change at all. She is attached to my gelding and could care less that this pony (another gelding too) was there.