Eventually at some point the difficulty will remain constant (after a drop), that is when the block reward does not outweighs the electricity costs of the mining operation anymore. What will happen at this point is not yet sure, but it is unlikely that the hashing power of the network will drop dangerously low, as there are still transaction fees and people who just like to participate (even at the loss of money).

Currently the hashing power will rise for some time to come as new faster ASIC are still being developed.

I wouldn't count on difficulty drop, even if it is unprofitable in the future. Please take a look at the current situation: mining is already unprofitable for the last year or so. And diff has raised 8 times since begining of the year...