1. ASIC Miners give up because of the difficulty and profitability (Difficulty Reduces = Scarcity Reduces = Price Decreases).
This is extremely unlikely, since even though it may not be profitable to purchase an ASIC, once the ASIC is out of the factory, it will be better to let it run than to dispose of it (of course, the "let it run" may come after being sold to someone else first). You can assume that pretty much any ASIC that is produced will keep hashing as long as it's still reasonably profitable to leave it on.
A USB Block Erupter, the least efficient ASIC miner, will still produce more than it consumes in power until the difficulty is at least 15 times what it is now and potentially quite a bit longer in areas with low power costs.
The difficulty explosion may reduce future (pre-)orders, but right now there is still a ton of pre-orders lined up waiting to be produced and to start hashing. And all these machines will actually get to the hashing, even if they won't earn back the initial investment, because it's still better to have some damage control than to throw it away. The difficulty growth isn't going to go away anytime soon.
