If you have a mossad problem, big integers were never going to save you from that before or indeed, after QC.
OTOH the typical cybercriminal wouldn't have access to quantum computers for a while so this is a pretty unscary prospect either way, for now.
https://blog.cloudflare.com/the-tls-post-quantum-experiment/ is a great read about a sample deployment of this by Cloudflare.
One of the things frequently intentionally neglected in Bitcoin discussions, is that it will die. It is guaranteed to die. It's a human invented digital technology, there is no long-term scenario where we don't kill it off through replacement and or competition. We'll be constantly inventing new cryptos, that process will never stop. The odds of Bitcoin maintaining its crown long-term are not good, for all sorts of reasons (not least of which are vast dilution through competition and regulation; eg nations heavily restricting foreign/external cryptos and only allowing official national fake crypto currencies (digital currencies), as China is speeding toward). We can and will replace Bitcoin with something better. And then we'll replace that too.
People that are irrationally, emotionally bound up in Bitcoin will fight you to the death to deny that. Bitcoin is not a forever technology, it's transitory. But who gives a shit about Bitcoin per Bitcoin, click, click, no more Bitcoin, I just moved my Bitcoin over to X blah coin that is better. The coins don't matter unto themselves, they're merely vessels for holding or moving value, nothing more. A crypto investor should always be prepared to abandon ship for something superior and maintain a rational independence from becoming emotionally biased toward a given coin. It's no different than understanding to not fall in love, so to speak, with stocks (or commodities, and so on).
The tragedy of Bitcoin is that as it fades away and gets replaced, it'll leave a giant environmental blackhole in its wake. There will be a question as to whether it was a mistake (was there a better alternative beginning technology for cryptos), or whether it was absolutely necessary to learn from to spark the field (and if so, was it necessary to go so far with it before abandoning it).
Besides the replacement factor, there is no scenario where major world governments allow Bitcoin to replace central bank controlled fiat currencies. Give up a huge source of their power, give up the ability to free-spend, 'print,' steal & paper over fiscal mistakes via inflation? Ha, yeah right. It's hilariously trivial for major governments to dictate financial matters within their own borders. Outlaw Bitcoin and throw a bunch of people into prison for using it and they'll instantly see 99%+ compliance, that's how easy it is to relegate Bitcoin to the fringe. All the largest economies are already priming their moves to squeeze crypto via intensifying regulation, to make sure it stays in the corner where they're willing to tolerate it.
Bitcoin is a speculative bubble and not much else.
The only hope it has is to be adopted as a reserve currency (not just legal tender) by many countries, and thus cement its value and then people will really be using it as a currency albeit on secondary layers, most likely provided by a number of centralised “PayPal-like” entities.
I don’t have faith in Lightning Network. Spend $50 to lock up $5000 where someone else can close you down and cost you $50 and you run around trying to find peers and be your own bank? No thanks.
So Bitcoin is a call option on this “hyperbitcoinisation” and anything less means it’s completely dead or just an occasional decentralised ponzi.
You sound like someone who sold all his BTC in 2012 and bought a 2nd hand Honda Civic with the proceeds, thinking you'd beaten the system.
This is why altcoins haven’t displaced Bitcoin: touting technological advancements over and above the benchmark set by Bitcoin is more or less irrelevant, except to the extent the narrative underlying it produces a network effect to compete with Bitcoin’s. But there’s no logical reason why Bitcoin’s network effect should ever be exceeded — Bitcoin has the first-mover advantage, and is the most widely recognized cryptocurrency, with the safest and simplest technical implementation which is clearly capable of meeting the needs of cryptocurrency users. Speculative value storage is the only real world use case of cryptocurrency, and Bitcoin does it better.