Realistically, when it happens a bunch of people will shut down their rigs b/c of electricity costs, then the difficulty will go down. So although the blocks will be only 25btc it will be easier to get them. Similar to what happened when the $ value of the btc crashed.
Since June, the dollar value of bitcoin has collapsed to 20% of what it was before. The difficulty is currently 200% of what it was in June. This means that buying new rigs right now is likely going to be very unprofitable.