Description of problem: The more people use Fedora, the more chances that something happens during upgrade - power can be shut off, or hdd may fail or whatever. The result is - system boots with errors and you can not do anything. How reproducible: Easily Steps to Reproduce: 1.Get previous version of Fedora 2.Start upgrade 3.Pull out electric plug Actual results: https://ask.fedoraproject.org/en/question/120596/boot-hangs-after-power-failure-during-system-upgrade/ Expected results: Page to direct people to.
DNF is not able to guess what happened and direct you to proper web page. It is on the user to look for solution, because they have more information than DNF has, at least in 'catastrophic' situation like you described.
Sorry for not being clear enough, but this is a feature request for documentation for dnf upgrade process, not about implementing smart logic in dnf itself. Users will look for solution and even could provide their own (if wiki edits are allowed for general public).