Fair enough. I'd expand that to say "code + consensus", which is what the rest of your post expands on. If the Bitcoin (for example) community really buys into the idea that we need to bail out some set of organizations, it's possible to execute a fork to do that. And the number of validating bitcoin clients out there is pretty large, so it would require a lot of buy-in.
It would have to be a hard fork (it would be possible as a soft fork, segwith-style, but the new coins issued would not be able to mix with pre-bailout coins unless clients updated).
To be honest, though, you're probably right. In my mind, depressingly so. The biggest takeaway from "too big to fail", even amongst progressives, seems to be that we have to shrink or break up the organizations that are too big to fail, rather than letting them fail -- only diehard libertarians and outcast Austrian economists believe that. The next time we hit this, we'll give the money to AIG to give to Goldman and buy Chris Dodd another house and move on with our lives while we get busy creating the next bubble (I think retail this time; that seems to be where the easy credit has relocated).
With a centralized model, there's no need for miners or mining, because you trust the system that you run. And transactions could be extremely fast.
Basically, it would look a lot like a bank with an API and public/private key signatures, running on a regular old database. Governments would probably love this, in fact, since it would prevent the cash economy from stealing their tax revenue.
You may or may not consider this "cryptocurrency", but then again most "blockchain" companies these days are just using it as a fancy database. Why do IOT devices monitoring production of $PRODUCT need to sync a blockchain? Why not just have them hit a REST API that is controlled by the client? Again, you can presumably always trust yourself/your company, so the trustless part doesn't add much value, and for a lot of this stuff there is no real need for consensus-resolution type functionality that the Bitcoin part provides.
If all you need is Merkle trees... those have been around for what, 40 years now? Bitcoin didn't invent them, Ralph Merkle did.
With crypto, you are essentially switching the authority figure from an elected government to a bunch of faceless miners forming an oligarchy.