As long as mining is profitable and the costs are reasonable, if we keep going like this then it wont last for another 8 years, imagine how many miners will be needed to mine by the next 2 halving? would you buy 100 ASICs to mine half a Bitcoin in a week?
Lots of people would buy 100 ASICs to mine half a Bitcoin in a week, if the price of one Bitcoin was $100,000...
It really all depends on the price of Bitcoin. Without the price rising, mining will indeed become less profitable. At some point there would be no more miners. We need to make sure companies continue to accept Bitcoin in order to grow the price at the same rate, or greater than the increase in difficulty!