It's hard to say from the symptoms pictured if this is due to root dryness or a disease like Southern Blight, which can proliferate in hot, damp/humid weather. You can look for the spore capsules (sclerotia) noted on the linked page, but not finding them won't necessarily rule out this or other fungal blight diseases. Root rot and crown rot can also wilt and kill Heuchera, as they are very sensitive to staying too wet. In the wild, they often grow in rocky habitats with very good drainage that skew dry instead of damp. Planting depth can also predispose them to root/crown rot, so make sure the crown (the main growth point, where roots and above-ground growth join) is at the soil surface and not covered by soil or impeded by mulch or leaf litter, which can reduce air circulation that helps to keep the crown dry.

If you feel the soil in the root zone of the wilted plants and it's not dry (test around four inches deep), then the plant might not recover, either due to root loss or infection. You can wait to see how they fare, but nothing can be done to encourage recovery (fungicide, for example, won't provide any benefit). If they don't recover in, say, a week, they probably would need replacing. If the soil is found to be fairly dry to the touch at that depth, watering them thoroughly (perhaps a gallon per plant, give or take) and see if the foliage recovers within a day or so.

Miri