I'm a newbie, but I had some grocery store buys with similar root health when I went to repot. I cut off all the roots that I was sure were dead (squishy, I left anything firm), staked the plant if it didn't have enough roots to support it, and got it into good media. None of the plants missed a beat. I misted the rootless wonders heavily every morning until they re-rooted. I'm not sure if the misting was necessary, but it didn't seem to hurt.
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