[njbchbum]

If the window box can be removed, try placing it in a shaded area [or put several of them inside in the air conditioning in a bathtub/shower area] and provide plenty of water to refresh the plant. Hopefully they can recover. If you must replant, I'd go with the suggestions of vinca, N G impatiens, geraniums, or even the wave petunia. No matter what you plant - that sun and heat are going to take a toll - you might have to water moderately morning and evening.