I have heucheras fade away here, and the way I renew them is to pull them out, improve the soil with compost and replant. Usually there's a woody stem to replant deeper than it was (here they tend to grow up out of the soil).

For as picky and miserable as they act while they're dying they actual rebound quickly when replanted. Even woody, rootless pieces do well and I think your potting up idea will work, but try a few right back into the bed and see how they do as well... it's less trouble and fussing!

Mine also always do better with a nice mulch.