I would try not to worry too much about the diabetes.
I'm sure that they would be more at risk after continuous eating of foods high in sugar (weeks, months), or having it in their diet every day.
If you are really worried, you could find out how much a blood test for diabetes would cost from your vet next time you go. at least that would put your mind at rest because you would know for sure, and be able to avoid sugars all together.
Ultimately, its happened already and there is nothing you can do IF they do develop diabetes. try not to worry! remember, degus can live with diabetes. I believe one of mine to have it (from before we got him from rescue) and he's been with us for over two years now with no problems.
I hope they're ok!