Harmonic balancer comes off

The replacement will likely go on easier than normal. If that worries you there are several formulas of Loc-tite that can ease your mind and help fill small voids and secure the bolt. If it's not a high RPM race engine and it doesn't vibrate run the sucker. Most likely you will need to replace the front cover seal. The Loc-tite should be allowed to cure before installing belts etc.... Just to be sure it was the whole balancer or just the outer ring?