I think that if a reorg fails due to an error while disconnecting blocks, the node should shut down.

My thought is that if we are trying to switch to a more work chain and something goes wrong before we can even try to validate that more-work chain, then we have a problem that is not related to the chain we're trying to switch to but instead related to our own hardware or software; shutting down and having the user deal with the issue is better than continuing on, when we know there's a more work chain that we're unable to try validating.

This has recently come up on testnet, where unpatched nodes are unable to reorg from the invalid chain containing the duplicate-input-in-a-transaction block, but rather than crash or shutdown they are continuing on the invalid chain, with messages like this in the debug log:

```
ERROR: DisconnectTip(): DisconnectBlock 00000000210004840364b52bc5e455d888f164e4264a4fec06a514b67e9d5722 failed
```
DisconnectResult DisconnectBlock(const CBlock& block, const CBlockIndex* pindex, CCoinsViewCache& view);
    bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pindex,
                      CCoinsViewCache& view, const CChainParams& chainparams, bool fJustCheck = false) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    
    bool DisconnectTip(CValidationState& state, const CChainParams& chainparams, DisconnectedBlockTransactions* disconnectpool) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    
    bool PreciousBlock(CValidationState& state, const CChainParams& params, CBlockIndex* pindex) LOCKS_EXCLUDED(cs_main);
    bool InvalidateBlock(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindex) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    void ResetBlockFailureFlags(CBlockIndex* pindex) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    bool ReplayBlocks(const CChainParams& params, CCoinsView* view);
    bool RewindBlockIndex(const CChainParams& params);
    bool LoadGenesisBlock(const CChainParams& chainparams);
    void PruneBlockIndexCandidates();
    void UnloadBlockIndex();
private:
    bool ActivateBestChainStep(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexMostWork, const std::shared_ptr<const CBlock>& pblock, bool& fInvalidFound, ConnectTrace& connectTrace) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    bool ConnectTip(CValidationState& state, const CChainParams& chainparams, CBlockIndex* pindexNew, const std::shared_ptr<const CBlock>& pblock, ConnectTrace& connectTrace, DisconnectedBlockTransactions &disconnectpool) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    CBlockIndex* AddToBlockIndex(const CBlockHeader& block) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    
    CBlockIndex* InsertBlockIndex(const uint256& hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    /**
     * Make various assertions about the state of the block index.
     *
     * By default this only executes fully when using the Regtest chain; see: fCheckBlockIndex.
     */
    void CheckBlockIndex(const Consensus::Params& consensusParams);
    void InvalidBlockFound(CBlockIndex *pindex, const CValidationState &state) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    CBlockIndex* FindMostWorkChain() EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    void ReceivedBlockTransactions(const CBlock& block, CBlockIndex* pindexNew, const CDiskBlockPos& pos, const Consensus::Params& consensusParams) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
    bool RollforwardBlock(const CBlockIndex* pindex, CCoinsViewCache& inputs, const CChainParams& params) EXCLUSIVE_LOCKS_REQUIRED(cs_main);