Long term mining (sustainability)

I'm curious about the sustainability of mining the currency long term (and thus of the currency itself). Like bitcoin, we don't mine all 21,000,000 coins until ~2140 or so, right? That's a long way off, but isn't it possible that long before then we'll hit a point where monthly mining cost exceeds revenue? That will vary by your local electrical costs of course, and also I'm not even talking about profit necessarily, just a break-even return (via TXN fees and/or a small amount of revenue) such that your electrical costs are covered by your mining operation.

I live in Seattle where electricity is $0.12 per kwh. I plan to continue mining Zcash indefinitely as long as monthly ZEC income is >= electrical cost, which it currently is. But this is easier today because we're in the first mining "epoch" where the block reward is at its highest.

I'm sure this has come up before, but curious to hear people's thoughts around this - wrt ZEC specifically.

I feel this is very similar to gold mining (except that the difficulty can go down), which has been profitable for thousands of years even for small (but illegal) operations like Galamseys. Once you scale out and hit initial ROI on your equipment, you will be able to start optimizing. For example, you can move to Grand Coulee or other parts of WA to push electricity down by 40%-60%, or use some sort of IoT solution to deal with cooling/monitoring/security. Mining will always profitable for those highly optimized operations. Also, even smaller operations could potentially stay profitable because of less overhead (business permits, commercial real estate, employees etc).

There is another option which depends on how much/if you think ZEC will appreciate in price in the future.

Similar analogy to @xalspaero but with raw materials (oil, coal etc) in that you can continue to mine it even when the market price is below your cost price, stock pile your coins then sell when the price goes back up again.

But this does assume you have the money to keep it running (primarily electricity costs) in the interim.