I had planted 2 coneflower seedlings in a raised bed in early summer. I am in zone 6, so our wintertime temps. can go down to -10. Will they die if I leave them in the raised bed over winter? If the answer is yes, is there a way to keep that from happening?

Coneflowers are pretty hardy so they should be fine. But a layer of mulch around them wouldn't hurt, just don't get against the crowns (stems) so they can still breathe.