I had the launcher minimized in the background, and was watching some YouTube videos, while downloading the 4.9 update.
I was also letting the NVIDIA control panel download, and then install, a graphics driver update for Windows 10.
All my other programs kept working (including Chrome and YouTube video) but the Epic Launcher, that was downloading the update, crashed when I brought it back to the foreground.
Under Windows XP, it wasn’t really possible to survive a live driver upgrade, but as of Windows Vista onwards, the WDDM absolutely makes this possible and expected behavior for well-behaved applications.