If the automatic transmission was rebuilt properly the rebuilt automatic transmission should last as long as a new one.
I've had a rebuilt transmission put in my truck 10 years ago and now It's gotten 150,000 miles on it doing some heavy towing and it's still going strong.
So if you have the transmission rebuilt completely and professionally or at least know what you're doing when rebuilding the transmission it should last from 100,000 miles to 300,000 miles.