Nvidia is down almost 50%... from its high around Jan/Dec. I suspect people saw this coming from a mile away. If you think the effect is likely to be stronger or weaker than the market predicts, bet on it now.
I'm sure the lifespan of used GPUs is reduced, but it's hard to say by how much. There's probably a lot of variability due to chip yield and operating conditions (especially temperature and ESD safety). But if I could get one at half off, I'd probably take that chance.
I believe miners are more likely to undervolt their cards and with running them at a constant rate, they won’t undergo the same stress from heating up and cooling down each time it gets used.
I sure hope those people bought mining GPUs/put their money where their mouth is.