Hebes are marginal plants in our western Oregon landscapes. Typically, the small-leafed varieties are more cold-hardy than some of the larger leafed cultivars.  But hardiness within the small-leafed group is also variable. The fact that both were affected seems to indicate an abiotic factor or factors, i.e., exposure to too cold a temperature, a poorly drained site, and/or too dry in extreme cases. You might take your fingernail or a knife and see if they are still green under the bark. If so, they may either come back on their own or would respond to heavy pruning to near ground level to force buds and new growth. Let me know what you find out. Below is a general article by Neil Bell, Extension agent and ornamental research scientist who has worked a lot with Hebes. He has said that if you get the right Hebe for a site, they are generally successful but if something about the site is off or there was a more extreme cold event, many are somewhat fragile. Hope this helps. Chip Bubl   OSU Extension Agent/Columbia County <personal data hidden> <personal data hidden>

https://extension.oregonstate.edu/node/80411/printable/print

https://www.pacifichorticulture.org/articles/late-season-hebes-for-northwest-gardens/