[comex]

Bitcoin has a self-adjusting difficulty rate. If blocks are being produced too fast, it increases the difficulty (i.e. average computational cost to produce a block), and if they’re not being produced fast enough it decreases it. Thus, it should never become impossible to mine.

There’s also the block reward halving process, which is separate, but in theory miners will still be incentivized to mine even after it hits 0, due to transaction fees. If not, well, the difficulty will go down until they are.