I think the market would tank but it would recover. I guess it depends on how it moved (all or some) and where it moved to (an exchange or a quantum computer hack).
I guess on a long enough time frame its bound to happen.
The coins are spendable. They are in your node's utxo database and the protocol allows them to be spent. Feature, not bug.
Therefore:
They can be spent. Assuming anything else is self-deceit, unless you are Satoshi and you know you lost the keys.
Any attempt from any developer to make these coins unspendable is a breach of protocol.
The owner of the keys to these coins can burn the coins if they don't want them: OP_RETURN will make them unspendable.
If you believe these things to be true, then if or when the time comes where we are faced with some sets of devs finding themselves VitaLARPing into benevolent dictatorships, your resolve shall be tested.
It would be a belt and the internet detectives would be excited. It would bring a lot of attention, but I don't think it would bring significant changes to the markets, for those who treat BTC as an asset.
OP_RETURN
will make them unspendable.