First, the way you phrase it is confusing and generally not how most would refer to that type of position. Better would be 'how I have been short Bitcoin for a long time'. Likewise 'I suspect no one offers very long dated put options on bitcoin'
Second, even if there were exchange traded/cleared bitcoin options with very long expirations (say 5 years), you would still have to consider the possibility that the exchange removes the product at a future date, either for lack of volume or other issues. While that might still work in your favor, it would not necessarily imply a bitcoin value approaching zero.
Of note, CME only has bitcoin futures out one year and futures options out three months (with very little volume). The bitcoin ETF BITO has options out to Jan 24 with considerably more volume/open interest. ETFs are not 24/7/365 vehicles but do have the advantage as likely to implode quicker than anything else (see USO)
As for removal, as long as I didn’t have to pay if they de-list the option I’d still put it on the books. I’m quite convinced of my position. As for selecting a more short term timeline, I don’t see my short position happening in the next 3 to 5 years based on block mining rewards so I’ll just have to continue waiting and watching for the day it becomes viable to put my own personal “big short” into action on Bitcoin.
Changing the hashing functions, encryption, and network verification are all built into bitcoin. It's designed to be resilient, and to use consensus when adapting over time.
It'd be really stupid for people to go "oh no, someone cracked sha256 and mined a million blocks, I guess we're done with bitcoin now. Buh-bye money!"
They'll fix it in the case of a noticeable exploit. If someone were clever, they'd mine blocks surreptitiously, sufficiently spaced out over time and different networks so that it looks like normal mining. They could get a few blocks per day for maybe a couple years until the upgrades. The impact to the system would be minimal.
On top of that, most of the ecosystem is built on specialized hardware that is designed to compute sha256 specifically and that cannot be swapped.
My 10 years prediction is based on a heuristic, the constatation that a generation of cryptographic functions tend to last 20-30 years.
I feel like it would be slightly unethical but on the other hand you're not really defrauding anybody. You did actually produce those blocks, not by improving your calculator but by using some other method.
Have fun raking in those free bitcoins. https://keys.lol/bitcoin
The Bitcoin core devs have been thinking about the failure modes of hash algorithms since Satoshi. If you are betting against Bitcoin primarily because you believe it will fail when sha256 inevitably falls, you are missing the bigger picture and underestimating the resilience of the Bitcoin developers and broader community.