Since Bitcoin is ultimately just software, there's a lot of situations where the network may fail temporarily, but could be fixed with a software upgrade.

I don't think those situations constitute failure. Tor makes changes to their protocol all the time in order to stay ahead of the game.

A true failure case would be:

a) ECDSA and all other digital signature schemes are broken, and there's no replacement.

b) All nation-states unite and restrict / ban all electronic devices. This is to kill all forms of PoW (bitcoin, monero, etc).

c) Apocalyptic event that sends us back to the stone age (can run nodes underground though).

d) A superpower rises up, eliminates all corruption period, and becomes so trustworthy that all commodities are abandoned for fiat.

The core concept of Bitcoin is just a distributed ledger of signed transactions and a PoW lottery for consensus on the transaction order.

That is a really tough thing to kill without wrecking the internet as we know it. And I don't think any other asset comes close in regards to competition. It's like comparing a filing cabinet to a computer.