Collectively, it is possible for too much money to be invested into Bitcoin mining, and the difficulty would overshoot so that all but the most efficient miners end up losing money...I fear that we're almost at that point and there will be a lot of pain for miners in the near future...It might be prudent to sit on the sidelines...and see how things play out over the rest of the year.
I disagree with the point of too much money being invested into BTC mining. Some people have the money to prop up even the most unstable ventures. There is also the YOLO factor, some deep pockets may drive difficulty up so far just to bring everybody crashing down in hopes that few will be able to recover monetarily.
There are also two special categories of unprofitable miners:
1-Those that have yet to realize sunk cost and continue mining out of desperation/blind hope/emotion/whatev.
2-Those that have a belief in the future value being greater than the current price and therefore continue mining in the face of unprofitable circumstances (a currently non-profiting miner taking profits in the future after holding/miners covering currently unprofitable mining with realized gains of past mining to weather the storm of unprofitability).
I do agree that the most efficient miners would stay profitable and difficulty can go through corrections.
Difficulty will always be pushed to the maximum limit until it is unprofitable for most. At that point it would retract, and since the network is not one unified brain it will overshoot the retrace and (aside from unprofitable miners) there will exist a void where miners will throw themselves at the network again until it is unprofitable.
People want BTC and there are only two was to acquire it...buying and mining. As long as is BTC is not fundamentally changed I believe there are too many people ready to buy "low" (a very relative term) to allow a crash large enough to bring difficulty with it.
As long as technology and ingenuity do not reverse I believe it is possible for the price to stagnate while difficulty continues to go up.
This is all just my speculation though, I could be wrong.