After I've quit eating a food entirely for a few months I start reacting to tiny traces of it. Like, I got sick from a 200 IU vitamin E pill made from soy. This has happened to a lot of people I've heard from online. You could try a trace after a few months to see if you have to be that careful.
Delayed food allergies may only last a few months, or they may last a decade or more. I don't know if it helps to disappear them if you avoid even traces of the food.
You can get enzyme-potentiated desensitization. Many people say EPD has helped with their delayed food allergies. The downside of EPD is that it requires very careful allergen avoidance for several days before the shot, and a day after. If you're exposed to allergens, you might get hypersensitized rather than desensitized!
A lot of gluten intolerant people have told me they stopped getting sick from gluten accidents after a while on a gluten-free diet. This doesn't mean it's fine to go back to eating gluten. It can be doing damage even if you don't get sick from it. And even if your body has entirely stopped reacting to gluten, the gluten intolerance could start up again.
Dr. Fasano, a celiac researcher, is developing a drug that blocks zonulin. Zonulin mediates intestinal permeability in celiac disease, so it might help celiacs recover or possibly tolerate gluten.
Going on a rotation diet may help prevent new food allergies from developing. Rotating foods means that if you eat a food one day, you don't eat it or any food that cross reacts with it until 4 days later. It keeps you from being constantly exposed to any one allergen. I do this, and it seems to have helped me. I developed new food allergies to about 5 foods that I didn't rotate, and only two new food allergies to foods I did rotate. But gastroenterologists don't usually recommend a rotation diet for people with celiac disease.
It's easy to develop nutrient deficiencies if you toss a lot of foods out of your diet. My fingernails became non-fingernailish in 2006. They were shredding to pieces on the ends of my fingers. So I wrote a computer program to keep track of my nutrient intakes, and used it to arrange a diet that takes care of as much of my nutrient requirements as possible. The rest I get from supplements.
Vitamin D may help. It's a hormone that regulates the immune system. It helps turn down autoimmunity, and celiac disease is an autoimmune disease. Many people are deficient in vitamin D, especially dark-skinned people or people living at high latitudes. Vitamin D is almost only in animal foods, like fortified milk, fatty fish and oysters. It's pretty hard to get enough from your diet, so supplementing with, say, 2000 IU of vitamin D per day may be a good idea. If people take more than this, they're supposed to get regular blood tests to monitor their vitamin D level.