There won't be any damage to your GPU directly unless you push it past the temperature or the power limits, or overclock it. I've run Folding@home on my laptop for 2 full years, and no degradation of any sort happened in that period until I tried to overclock the VRAM. Even after that, it eventually recovered by itself so... The thermal paste degraded within 2-3 years when I wasn't using it properly, but this time it was fine all the way till the end.
What can happen is the power adapter can fail from sustained power load(laptops aren't designed to run under heavy loads 24/7), and if there's a power surge from the power adapter that hits the components under full load, that can kill your laptop. That's how mine died, very recently. I was running two threads of XMRig on the CPU and Folding on the GPU, I'm sure the motherboard wasn't designed to be able to handle that much power draw for long periods of time in the first place. The power adapter's always been acting erratically, but this time it fried the motherboard. The truth is, that could happen anyway, regardless of whether you're mining or gaming at that instant, it's just that the probability of failure can increase with all the time you're plugged in and pushing it hard. It's all about risk : reward. There is an element of risk involved, however minor, and if you can't afford to get a replacement, you shouldn't do it.