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
```
CFeeRate oldFeeRate(mi->GetModifiedFee(), mi->GetTxSize());
                if (newFeeRate <= oldFeeRate)
                {
                    return state.DoS(0, false,
                            REJECT_INSUFFICIENTFEE, "insufficient fee", false,
                            strprintf("rejecting replacement %s; new feerate %s <= old feerate %s",
                                  hash.ToString(),
                                  newFeeRate.ToString(),
                                  oldFeeRate.ToString()));
                }
                for (const CTxIn &txin : mi->GetTx().vin)
                {
                    setConflictsParents.insert(txin.prevout.hash);
                }
                nConflictingCount += mi->GetCountWithDescendants();
            }
            
            
            
            if (nConflictingCount <= maxDescendantsToVisit) {
                
                
                for (CTxMemPool::txiter it : setIterConflicting) {
                    pool.CalculateDescendants(it, allConflicting);
                }
                for (CTxMemPool::txiter it : allConflicting) {