Is surgery the best option for a torn posterior cruciate ligament?

It depends. This depends on the degree of the tear, associated injuries, and the type of activity that you desire to return to. Generally, partial and low-grade isolated PCL injuries can be rehabbed and braced. High-grade or complete PCL injuries or lower-grade injuries which result in persistent instability may be better treated with surgical reconstruction. Talk to your orthopedist regarding your situation.
Not Necessarily. Often a PCL injury can be treated with bracing and physical therapy. It depends upon other pathology within your knee, and your functional requirements.
Not Necessarily. This is a hard question to answer without more information. The answer depends on the left of physical activity. If you participate in sports, or any activities that require you to shift the direction you are moving in, very quickly then surgery is the best option. For normal activities such as walking and even occasional running PCL is not necessary. At best you might need a brace for running.