Is it possible for the bursa sac in the knee be destroyed?

Probably not: Knee bursitis is inflammation of a bursa located near your knee joint. A bursa is a small fluid-filled, pad-like sac that reduces friction and cushions pressure points between your bones and the tendons and muscles near your joints. Each of your knees has 11 bursae. While any of these bursae can become inflamed, knee bursitis most commonly occurs over the kneecap or on the inner side of your knee.

Several bursae: Usually we don't use destroyed for a bursal sac. They can become inflamed. There are several about the knee. The largest on is in front of the kneecap.