Is there is few miners, there is bigger rewards for those few... also, the higher the BTC price goes, the higher the reward, even if it little, it is enough because BTC price is high...
So i am really not worried about that, also when the time comes, there is going to be enough alternate blockchains and altcoins to rely on, and computer power will be enough for anyone to mine even for little reward... Things will change, this technology is here to stay and there is nothing that can stop it...