Remove the PCIe fan(s) from the radiator (4 screws) and reattach to the case where they were located prevously. You still need the fans to cool the PC.  You just take out the GPU and the radiator.  The PC still has the front case fan even without the liquid cooling option.  There's no F1 or C or something to continue option despite the fan failure? 
I have an Area-51 Threadripper R6 that I configured with the dual liquid-cooled GTX 1080 cards.  I have loved it for VR since I took delivery in 2018.  No issues, runs like a champ - until... I chose to upgrade my VR headset to Vive Pro 2, and in doing so learned I should upgrade to an RTX 3080 Ti for best results.  Ok, got that, arrived yesterday, and thought the GPU swap out would be simple, but no... I found that removing the dual liquid cooled GTX 1080s, with their attached fans, now cause the Area-51 to complain about the PCI fan now being absent, and it won't get past BIOS.   Do I buy a fan module from Alienware to address this, or is there a better option?  Anyone else have this issue?  
Area-51 R6, how to upgrade the GPU dual liquid cooled Nvidia 1080s?