There's no telling how long remission will last after a resection. Like the disease itself prior to resection it will do as it darn well pleases and remains very individualistic.
That being said, just as some encouragement, I had a resection of 18" of the mid-ileum in 1978 and then was blessed w/a 20 year remission of disease activity and symptoms. Since its return the disease has been quite mild overall and I've varied between symptomatic remission and minor flares the last 9 years. I've been on Imuran the last 4 1/2 years. I would seriously consider Imuran or 6MP after a resection to help ensure the longest possible remission.
There does seem to be a trend that when Crohn's does return after surgery it tends to follow the same pattern as when it first occurred. There also seems to be a trend that as we get older the Crohn's flares appear to be milder. But neither is a hard and fast rule. The first certainly didn't occur for me but the second does seem to be holding true for me.
Some people are like Slinkies... Not really good for anything, but they still bring a smile to your face when you push them down a flight of stairs.