Yes, the tubular sleeved stomach can stretch. Yes, the stomach pouch of a gastric bypass patient can stretch. Stomachs are made up of smooth muscle, which is capable of stretching.
My sleeve definitely has a greater capacity than it did during those first few post-op months. Plainly speaking, my sleeve can accommodate more food now. However, anyone who expects tight stomach restriction by itself to prevent overeating may be engaging in unrealistic thinking.
At this point, the quality of food I place into my mouth is more important than the size of my sleeve. A person with a thumb-sized sleeve or golf ball-sized bypass pouch can and will regain all his/her weight if too many slider foods (e.g., chips, cookies, crackers, pretzels, ice cream, popcorn, donuts, mashed potatoes) are eaten.
Slider foods do not produce a feeling of fullness or satiety. Therefore, a person who is determined to eat around the pouch or sleeve can accomplish his/her mission by overeating sliders. My personal saying is, "The road to weight regain is paved with Lays, Doritos, Ruffles, Ben & Jerry's, Fritos, Oreos, Breyers, and Chips Ahoy."
It is all about choices.