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
```
bool Condition(const CBlockIndex* pindex, const Consensus::Params& params) const override
    {
        return ((pindex->nVersion & VERSIONBITS_TOP_MASK) == VERSIONBITS_TOP_BITS) &&
               ((pindex->nVersion >> bit) & 1) != 0 &&
               ((ComputeBlockVersion(pindex->pprev, params) >> bit) & 1) == 0;
    }
};
static ThresholdConditionCache warningcache[VERSIONBITS_NUM_BITS] GUARDED_BY(cs_main);
static bool IsScriptWitnessEnabled(const Consensus::Params& params)
{
    return params.vDeployments[Consensus::DEPLOYMENT_SEGWIT].nTimeout != 0;
}
static unsigned int GetBlockScriptFlags(const CBlockIndex* pindex, const Consensus::Params& consensusparams) EXCLUSIVE_LOCKS_REQUIRED(cs_main) {
    AssertLockHeld(cs_main);
    unsigned int flags = SCRIPT_VERIFY_NONE;
    
    
    
    
    
    if (consensusparams.BIP16Exception.IsNull() || 
        pindex->phashBlock == nullptr || 
        *pindex->phashBlock != consensusparams.BIP16Exception) 
    {
        flags |= SCRIPT_VERIFY_P2SH;
    }
    
    
    if (flags & SCRIPT_VERIFY_P2SH && IsScriptWitnessEnabled(consensusparams)) {
        flags |= SCRIPT_VERIFY_WITNESS;