"If, however, some content appears in the chain that causes significant risks, we can fall back to the reactive method, which is a retroactive chain reorganization to invalidate the offending block (and any subsequent blocks) while immediately activating the new rules." From

GitHub

BIP 110: Reduced Data Temporary Softfork by dathonohm · Pull Request #2017 · bitcoin/bips

Mailing list thread at https://groups.google.com/g/bitcoindev/c/nOZim6FbuF8 Editor note: please post conceptual feedback and meta-commentary on th...