Not to go through with the amputation when there is already gangrene will likely end in an unpleasant and painful death.
However, there is a bigger issue. The loss of circulation that leads to gangrene that leads to amputation, usually affects more than 1 limbs, so your other leg is also potentially at risk.
The most important thing will be to have good control of your diabetes. By taking insulin and controlling your diet.
Not an easy place to be in. I wish you well.
Sorry your at this place to have to choose. yes, it would would be a very painful death from gangrene infection. There are lots of people that have a great life that have lost limbs. look at the survivors of the Boston marathon bombing. Its not the end to loose a limb... dieing is the end.