Was it sudden death or did this happen over a period of time between June 03 and now? What kind of watering? Too much and it can get root rot in soils not draining well enuf and not enuf water can cause wilting if not too well established. If the soil is very well draining like mine is I did notice my creeping thyme (T. serpyllum) needed a drink now and then especially during July/August when we had absolutely no rain at all, but that was the first year.
Tell us more about your soil and moisture conditions. Was any herbacide used nearby?

Vera

LynneNy - whoa, that is sad! Did you fertilize your thyme by any chance? Looks like it could be nitrogen burn from fertilizer.

Thanks for the responses. No fertilizer was used near here. I just noticed it today. We have had short heavy thunderstorm downpours the last 3 days, but I thought this area was pretty well drained. The soil is a mix of our natural clay soil, some potters mix and a little compost. It seems like this happened pretty much overnight. Should I cut away the bad area in hopes of salvaging what is still green?

Try digging down in the soil after it's had a chance to dry up some from the rain and see how wet and or sticky your soil is.
Does potters mix mean potting soil? You might of added more water holding capacity to your natural clay soil rather than supply drainage OR your ammendments were not dug in and incorporated enough...you want to add ammendments that have bigger particles to help create more passages for water to drain. Check out the Compost, Soil and Mulch forum for ideas.. I do know that lotsa folks who have added sand to certain clay type soils ended up creating cement. Compost works if you add enough for the area and depending on soil type you might add more or less.
I hope you find your answers...that was a pretty nice looking plant! Cant hurt but to give it a try and cut back to the healthy parts of the plant/s and give it a whirl.

Vera