cut the flowers off and they will regrow to use again..really its best to keep cutting them back and to stop them flowering ..i never use mine they are in bloom at the moment and look lovely..
Sure, the chives are useable as long as they are green. Additionally, if you do let them flower and don't cut them, they go to seed and spread like wild fire...
You CAN eat the flowers of course,they look lovely in a salad;they still have a Chive taste but quite a bit stronger.Handy if you have forgotten the spring onions!