The fact that the counselor has left the unit has no bearing on this situation. Counseling statements are simply formal records of an event. These records can be used, in most circumstances, by the chain of command when making decisions concerning personnel actions (i.e., promotions, bars, flags), disciplinary actions, or corrective training. If this counseling statement was meant to correct a serious or on-going issue then yes, it can probably be used for any of these reasons.
If the issue cited in the counseling statement has been resolved, however, it may not be able to be used as documentation to support one of these decisions. See Are resolved counselings still valid? for details.