Question for Dentists/Tooth experts...

It all depends. A root canal is done because bacteria has gotten into the root of the tooth. That doesn't mean that you have infection/abcess now (that's why no pain), but you will, 100%, have it in the future if you don't clean it out now.

You may have been able to put off the root canal if you had the tooth refilled right away. Or maybe not. It may have come loose because of new decay underneath that filling before it came loose.