I have a chive bush that has been growing steadily for a year now, never gone to seed and provides plenty of chives for my use which is hardley unless it is potatoes. You can always plant the green onions and see what happens.

I have 1 chive plant that is probably 12" dia. It comes back every year with NO attention and produces enough to supply 5 households with more than they can use. I even take cuttings and give them away at work. When I let it flower I cut those and bring them in to a vase. I love the way they make my kitchen smell.

Well, if you do not harvest chives then they will flower and grow seeds
and disppear for a while then come back next year, in zone 8.
In cooler zones they can stick around all summer and beyond.

As said, Chives will make a very easy to grow perennial plant, you will get Chives year after year. Cut some off and more might grow this year.

As for "green onions", if you mean bunching onions that never form a bulb, you could plant them then cut them off and see if more grow from the root cluster and see if you can get them to grow until winter. They grow all thru summer and fall in the Midwest but will taste rather strong, still good for cooking and stir-fry but you may not like them raw. They survive thru winter and grow again, but I never really like the quality of them so I get rid of them. Always have best quality the first spring to early summer IMO.