Hummersteve:
The only problem I have had w/S.greggii was downy Mildew that was years ago it does defoliate and kills the plant. Botrytus can be remedied by Daconil.Which is rated for vegetables.That is the safest way I know to deal with it.
Art

First step is to make sure you've identified the pathogen correctly. Is there the tell-tale grey mold present? For most rot I'd re-pot it in sterile soil mix, cut the greggii back to the stump, then douse the whole thing with 3% peroxide. Then if it resprouts, make absolutely sure not to splash soil onto the new greggii leaves while watering, as you try and disrupt the infection cycle.

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dicot

No I have not for sure ID anything . But the seller suggested that was the culprit as that is what they have had happen to this plant greggii pink preference. All the leaves turned to crispy critters and fell off the plant and there have been no signs of life but I will try your suggestion. It looks dead so nothing to lose.

I find that blackleg (Pythium) can do in Salvias, especially cuttings

Here is a link that might be useful: Pythium Root Rot on Ornamentals