If circulation is caught early, can dry gangrene be prevented or not?

Risk can be lowered. Signs of peripheral artery disease (pad) are: pain in the calf muscle with walking that is relieved with rest, pain in the foot at nighttime that improves with standing, and poorly healing foot or ankle wounds. Diagnosing pad, determining the severity of disease, and treating it appropriately (risk factor management and/or intervention) can help lessen the risk of developing gangrene.
Yes. If there is circulation problem it can be dealt with before problems occur. Sometimes medical management is all that is necessary but sometimes an invasive procedure might be needed. Not all circulation problems are equal. Talk to your doctor to see what you need.