Aluminium smelters will still be there and working (barring some unforeseen major global problem in the Aluminium market) in 10 years time and well beyond.
Cryptocurrency miners? Well Bitcoin is all but past the point of being profitable to mine, whilst also now being blocked from being traded or used as a currency in a lot of major market places. So in 10 years, it will probably only be a hardcore still using/trading it. And they wont be mining it anymore. Other cryptocurrencies? Well since people finally are beginning to wake up to the scams, I expect that the bubble wont be too long in bursting. 10 years time? I have my doubts if it will still be such a power draw.
Now if you're the power company supplying electricity in this area, and you have a choice of supplying an industry that maybe uses a little less electricity, but is guaranteed to be there long term, or an industry that might use a lot of energy now but is definitely only a short term prospect. You would definitely always go for the long term option. And this IS an either/or situation - investing in more energy generation capacity is very expensive and takes years to come online. You're not going to make that investment based on the crypto mining bubble. Well not unless your either crazy, or have drunk the crypto currency kool aid...