If you had a root canal there will be no pain if the crown comes off. If the crown came loose after flossing it is probable that there is decay under that crown. You should have it checked so as to avoid the loss of the tooth
It's really difficult to answer your question without a photo. You don't mention if these are old veneers that are being replaced or new ones that you don't like. Also, doing 6 restorations is usually not ideal. I usually suggest 8-10 on the top arch to allow the dentist to create a more ideal...