I have a USB-C/3.1 Gen 2 header cable running straight down from the top of the case to the USB 3.1 Gen 1 adapter and it goes under the CPU cooler.
If it's built to UL and, I have to imagine any other world safety standards, it has to use insulation that will withstand contact with whatever hot surfaces are present inside the case. So short of catastrophic failure or incredibly off-standard and cheap wiring, it simply won't melt in the short term.
I'm not sure what CPU you have, but the highest temps on the CPU die will probably be about 95C since that's Tjmax for most modern CPU's. So with that in mind, everything...