You can only assess their status if you have an ultra sensitive MRI scanner such as the one used by Prof Taylor or other means of testing them eg post mortem staining; or other indicators such as measuring their insulin production. Obviously I don't personally have any of this kit or access to these tests which are only available to world renowned scientific researchers such as Prof Taylor & his team. I just have to read the findings in their reports published in acclaimed scientific journals (such as the Lancet & Diabetologia) & take their word for it.
This evidence is good enough for the world's foremost diabetes experts so it is good enough for me.
"The study found, however, beta cells are not permanently damaged in early T2D and can be rescued by
removing the metabolic stress of excess fat within the cells. The findings are the result of the examination of insulin production on a subgroup at baseline (starting weight), immediately after weight loss (five months), and upon follow up of one and two years."
https://www.diabetes.org/newsroom/press-releases/2019/insulin-producing-beta-cells