If there is no viable alternative to EC for public key cryptography by then, a lot of things will break down, and Bitcoin wouldn't be my main worry.

If there is, I hope Bitcoin will have transitioned.

Actually no.

Long answer: Yes, the outgoing transaction from a ledger to another one is done using crypto that can be broken by quantum computers. But a ledger that has never been used to send money is only visible by it's hash value. So it's security is based on sha256 which is quantum secure (There is Grover's algorithm, but it should be OK for a while). BC would just need to change the signing algorithm. So unless quantum computers pop up just over night everything should be fine.

There are many threats to Bitcoin, IMO QC is one of the smallest.

There are a few ideas about how to circumvent that, most are pretty early. I think the general consensus is we still have at least 30 years to figure it out as that kind of quantum computer is more than likely, that far off. But of course it can all change pretty quick.

And if we don't have quantum cryptography by then, not just Bitcoin, everything we use today pretty much will be at risk.

No, they would probably move to a postquantum cryptography system.

I would imagine the security of your traditional bank account would be at risk as well.