While I think that it's quite unlikely now for bitcoin to "fail", I personally think that what would cause bitcoin to fail completely is if a certain person finds a catastrophic bug and abuses it instead of reporting it to the devs. Probably a bug that can make people steal bitcoin from certain addresses or something along those lines.
If too many miners can't make a profit btc dies.
It is one of the major flaws in PoW design. (Insane Input Costs to maintain it's network.)
I don't think so. As long as a few full nodes are running then bitcoin is fine. I also think having zero miners is very unlikely, as there's always money to be made regardless of price. Worst case scenario is just that the number of miners will significantly drop, but probably not necessarily comes down to zero miners.
If no one makes a profit , then it becomes zero miners and btc dies,
If a few can make a profit of course btc lives on, but more centralized than it already is.
The Possibility no miner makes a profit depends on the marketplace.
After all how many New atari consoles do you see made nowadays or 8 track tapes, no profit and these companies quit producing more.
Worst case scenario is that
No miners can make a profit.
Anything else is painful for the miners, but survivable for btc.
FYI:
It takes Millions of Fiat Dollars per month to sustain the btc network,
otherwise the 51% attack becomes a greater possibility and it finishes off any support for btc.
Many btc fanatics don't like Proof of Stake, but those insane input costs are not a danger to a proof of stake network.
As it is not geometrically wasting more energy like a PoW network is, with no real benefit to show for it.
