Hello I live in France and have done for the last twenty five years, diabetic treatment has always been very good and is 100% covered, been on an insulin pump for more than 18 years and have had the libre for the last 2.5 years, you will need to get a carte de sejour to work in France after brexit and then you should be able to get your carte vitale and that will depend on how difficult the U.K. makes life for EU citizens living in the UK but I do not think you should have a problem if you are working in France, I find living in France so much better than the UK