<< Does using multiple displays reduce the life of a GPU? >>
generally speaking, no.
Once the screen is drawn, refreshing the screen every 60th second or do is done by a hardware automaton that fetches the data out of the display RAM, and serializes it and sends it to the display over the connected cable. It is a fairly high data rate, but does not tax anything but the display RAM memory, which the card can support several displays at once without stress.
What is somewhat more heat producing is that HDMI runs at 5 Volts, where DisplayPort Runs at 3 Volts. Again, not a big deal. What IS a Big deal is the HEAT generated by an adapter TO HDMI. Consider the possibility the adapter is what has failed. Also, adapting the card's DVI output to HDMI is a MUCH simpler, cheap, passive adapter.
There is a lot of complex screen drawing, scaling, and shading power on these cards, as well as a lot of RAM memory, and failure rates are a function of the complexity of the cards, the number of connections between modules, and Heat generated.
They get hot and die. Don't take it personally.
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if you replace that card with a Metal-capable card, you could use 10.14 Mojave.
