I think that if there were flowers and seeds, they may replant and grow new ones. This happens with oregano here. Because your in Z5, you may not see any new growth until about June.

I am in SW Ohio with 60 thyme plants as ground cover atop a long stone wall. They thrived spring, summer, fall, but now that the snow has melted I see that every single one is totally brown. Please tell me that means they are dormant and will come back and not that they have all died.

My thyme does not turn brown in the winter. It appears alive although its winter color has some purple to it but never brown. Do not do anything now. Wait for the warmth of spring to see what life there is in your plants.

Just so you know, the first winter is the true test for any plant north of the frost line. If you wind up having a lot of loss, you will need to see if something else will do better there for you. It may be too cold, not enough drainage, wrong kind of thyme for climate, and so on for your planting.

FataMorgana

Give it a little more...um...time. Mine is in large cinder blocks near out apartment building and the outer leaves turned sort of a purple-brown, but the center of the plants are still green. They were covered with snow most of the winter and I didn't think they'd survive in the cinder blocks since the blocks were moved late fall and roots severed to do so, but it looks like they have. Of course, I don't know exactly which thyme I have as I dug it up from an old herb bed at an old farm house we were renting several years ago(so I suspected it was hardy).
Did you start them from seed or did you get them from a local nursery? If from a nursery, they're probably hardy for your zone.