Hi. Very sorry that your son is going through this. I was told that blockages occur sometimes and that if it cannot work itself out within 24 hours, that surgery is necessary. My surgeon said that it is a standard rule not to "let the sun rise and set" on a blockage -- that if you need the surgery, it should be done quickly. I just mention this in case this came up very suddenly and you feel rushed. It's normal to rush into the surgery.
I think that the blockage risk is always there with anyone who has had abdominal surgery. It's just luck of the draw, I think, whether it happens. I was told that sometimes you can feel it coming on and if it's mild, you switch to liquids or just don't eat or drink for a while and it can work itself out.
I don't think that if it happens once it means it will happen again. This could very likely be a one-time thing. There should be statistics on this that the surgeon should be able to provide you.
Sending good wishes for the surgery.