It's probably a good time to lift and divide, then replant..

Die-out of woolly thyme over winter is very common in colder areas that receive lots of snowfall and plentiful winter rains. The soil just stays too wet too long for it to be perfectly happy :-)

OK, I will attempt to divide and be more vigilant about trimming. Gardengal, is this kind of center dieback what you see as a result of environmental condition, and that can't be helped by cultivation? I don't think this is a case of the soil staying wet as it is practically sand under the pavers.