I had Gestational Diabetes when I was pregnant with my daughter just over 2 years ago. It was managed purely by diet (GI Diet), and luckily it 'vanished' after I had bubba. I recently started with a new doctor who I had to give my medical history to and when the topic of my gestational diabetes came up, he bluntly said "You will have Diabetes later in life" (or words to that effect). I am hoping that by losing weight and getting into shape, I will avoid Diabetes later in life.
My Dad was diagnosed with Diabetes about a year ago (Type 2). He manages it through diet and pills. The pills upset his stomach a fair bit (I think its the same with all pills for Diabetes). He has a good hold on it now and he knows what he can and cannot eat and what effect different foods have on his blood sugar levels.
Diabetes isnt a death sentence by any means, just take all the advice you are offered and you should be able to manage it quite easily.
Have a good day