If it's a grade III injury (i.e. full thickness tear), it is almost always repaired. Grade II (partial tears) are the gray area. Some are some aren't. Depends on degree of tearing and whether or not there is instability.
It depends on the grade of tear (II or III) and location (origin, midsubstance, insertion), as well as concomitant injury. Usually, isolated PCL tears are the least deleterious and, for the most part, are treated conservatively.