Unless you like philosophy and having a lot of imagination, there is not much to worry about at all.

Bitcoin is not like a military base.  You can shoot rockets at a military base but they will know, and even if they do not because they die before they find out, everybody else will know.

Bitcoin can be attacked behind the scenes with absolutely no body else knowing it.  Quantum Computers have been the subject for years now, but remember there are a lot of technologies and science experiments done privately with no public eyes to see the results.  This means somebody somewhere in this world may have already broken Bitcoin a long time ago but we only have not heard about it yet.

An attack like this is closer to a trojan horse.  Bitcoin can be broken 'from the inside' and hell only breaks loose when the perpetrator wants it to.  Or, we all get lucky and the perpetrator is actually going to help Bitcoin get better instead of trying to destroy it.

What does this mean?  It means there is no point in fearing what could happen in the future.  For all we know, China may secretly have a Quantum Computer 100 times faster and better than what is publicly known to be the best today.  They may have already broken the entire thing.  In fact, it would be in THEIR advantage to never speak about it publicly.  By breaking encryption, you can spy a lot better.  You can find and put together information you never could have before.  Mentioning it publicly means everybody else starts preparing to secure themselves and their privacy in the face of Quantum Computing.

If this ever happens to Bitcoin, it will be fixed as soon as possible through emergency measures.  It would not be a matter of 'is X better than Y', it would be a matter of 'X is not Quantum ready, Y is'.