I can verify that it goes unranked and ends immediately if Spy and Killer both kill eachother n1. Doesn't make much sense how they both kill eachother, but it can happen.
An example of why you don't nk with both scum alive, and this was the 1/3 where it really was agent. More often than not, it'd go even worse than this.
To settle the issue once and for all: yes it goes unranked if spy and killer hit each other n1 (past n1, it stays ranked), but it takes a heart from you anyway and counts as a loss on your pie. However, you can file a report and a mod will refund the game without hesitation.