Post major operation is it common to die from blood clots in the brain?

No, uncommon: Blood clots are uncommon after all surgeries. However, when they do occur they are usually filtered into the lungs and people can die if they are large enough to block enough of the lung. However, the risks of this are small, but how small depends on the surgery and how it is performed. For more information see your physician. In addition, there are many other risk factors to discuss with your md.