I think the answer will be similar to 'how long is a piece of string', as people can vary so much and it would depend a lot on how damaged your beta cells were. Even with the best will in the world, some people will need the support of medication, although it may be significantly reduced by sticking to a good diet and getting plenty of exercise 🙂
Although I am T1 on insulin, this fact clearly shows me how beneficial regular exercise is since my insulin requirements reduce significantly when I am exercising (and increase when I am not, as at the moment because I have a bad cold!). Personally, I consider 'regular exercise' for me to be around 90 minutes a day for 5 days a week (sometimes more, sometimes less, but that is probably the average). I have read experiences here from many people who have sustained good control without medication for many years - whatever you achieve, your control will be better and medication requirements smaller if you are fit and healthy 🙂