My greatest praise for Linux is that it's nearly impossible to completely brick the install - it's almost universally possible to recover it, no matter how broken it seems. You can potentially live-boot your XPS from a USB stick, chroot into your existing install and let the upgrade run to completion (Google around for some guides). 18.04 is a very slick OS - I'm running it at work on my company Precision laptop and it's fantastic. The '-d' flag is required until the 18.04.1 release, which is when the new LTS is considered stable enough for existing LTS users to upgrade.