What should a diabetic and hypertensive patient who tends his sheep in the desert, fearing for them loss, hunger, and thirst, do: should he fast in Ramadan or break his fast and make it up later?

Ramadan fasting is obligatory for every accountable individual, unless they are sick and fasting would harm them or worsen their illness. In such a case, they are permitted to break their fast and must make up for it later. If the illness does not permit breaking the fast, but fasting causes you extreme hardship and you fear harm due to your work, which cannot be postponed, then breaking the fast is permissible. You must form the intention to fast the night before, then break your fast when hardship occurs.