Windows can handle itself without a proper GPU driver. Although the resolution might drop to something like 1024x768 if it fails to detect and auto-install drivers - that's fine, you're going to install it manually anyways, nothing to shake about.
To fully and properly wipe out current driver I'd recommend using a DDU (display driver uninstaller) - a utility that allows to reboot into safe mode and fully erase all traces of video drivers ever been installed in the system. When you first start DDU, if it doesn't show a dialogue window to choose startup mode, go to options and check the "safe mode" (enable safe mode dialogue or smthing, idr how it is fully called and I'm not near my PC now). Alternatively, there's an AMD specific utility to erase driver installation in safe mode, but I prefer DDU (although used both, work fine).
As for CRU (custom resolution utility), it's a tiny bit more complicated software, but you can ez get along with it. In CRU, find your current res, open it and screenshot/write down the parameters. Then, by trial and error (I'd explain thoroughly with screenshots, but I'm really not at home) make a resolution of, say, 1920x1080 with the same other parameters. 1920x1080 (16/9) is not exactly same as your 4096x2160 (18/9), but close enough for test run. See if it shows in resolutions. If CRU seems 2complex4u, either try DDU first or I'll be back home in 5-6 hrs and will give instructions with screenshots.
Also, have you tried just installing earlier driver version with factory reset being checked in advanced settings?
