Just suppose...
What if bitcoin seems to average about 7500 USD or so over a very long period, like a year or even more. Currently, this isn't high enough of a value in USD to really mine anymore with GPU's, if mining for profit in USD anyways. I do not mine with ASIC miners and I really know very little about them, even though I almost bought a Bitmain Antiminer S9 before I build my 8 GPU rig.
Will mining taper off to little to nothing, will difficulty levels be adjusted to compensate miners, or what else?
I would be interested to know some thinking on this, should it become a reality or even close to a reality for some length of time.
If you found that your current miner no longer be able to mine the coins with profitable rate then you should plan accordingly for that you should move to ASIC miner or just mine other coins with your GPU miner since there are lot of worth coins available to mine with GPU and you can convert them into bitcoin which is more profitable than direct mining of bitcoin.