That's ok, Ethereum is down to half of what it was a little over a week ago, Monero is also down to less than half of it's high price in the last month, etc. When Bitcoin has large swings up or down it tends to drag the whole crypto ecosystem with it.
Ethereum at $700 would have be crazy profitable 6-8 months ago, but it no longer is, due to increased difficulty. You might scrape a little profit there, but in June that would have represented ~$10 in profit a day on a 1080TI. Now it's maybe $2.
Maybe, maybe not. I've still got 2x machines running old 7950s which were mined with for over a year and they're running perfectly fine.
Gaming and general computing is such a low intensity activity - if they didn't break while they were mining I figure that they're comprehensively stress tested at this point and they'll run til they're too old to be useful.
The biggest problem that mining GPUs tend to all suffer from is fan failure. I'm speaking from experience.
Replacing a video card's fan is certainly doable, but it isn't nearly as easy as replacing a CPU or case fan (due to the fact that so many GPUs have custom fan setups).
Some of the GPUs (like Sapphire's) have fans which are easier to replace. These are not the norm. Also, being easy to replace doesn't mean they are easy to acquire.