Oh yes, reholster immediately if the threat is over. IF, you removed the threat, try to get anybody that's not running from you to secure that immediate area and wait for PD. Have them help keep people away from where you were, where the shooter is, and try to get calm again. Don't touch anything, raise hands when PD arrive and tell them who you are, and where your holstered gun is, etc.
Odds are, you'll be treated fine.
Of course, if you're in NYC, Chicago, and your bravery saved the Mayor, you'll still get life, just for saving lives.
Go figure.