Actually, a diabetic friend of mine (in Leeds, where the CCG seems to have an abundant amount of cash. I'm seriously thinking of relocating) just had a gastric bypass. She had to "follow a special diet" for three weeks before hand to "shrink the liver", but when I looked over the sheet she'd been given, it was very clearly a very-low-carb diet.
She was plunged (as we know and see all too often) into an immediate state of keto flu, couldn't keep warm, couldn't stay awake. But even before the operation, her Hba1c was the lowest it had ever been in 15 years, her liver had shrunk "to normal size" and she'd lost 3 clothes sizes.
This was just run-of-the-mill NHS treatment and, I have to admit, I was impressed. It was nice to be able to explain to her what was happening in her body, why the diet was working and how to ease the keto flu symptoms.
Now, 3 months along, she's lost 6 sizes, her energy is back, her arthritic pain has significantly lessened, she's still off the carbs (though less rigidly so), and her consultant predicts she may never have symptoms of diabetes again.
Honestly, given the option and having seen what it's done for her, I'd leap at the chance for surgery.