A red "X" means that a certain person died.
If you fail the password on day 10, you simply lose two people. I recommend to read on, because the "bad ending" paths are part of the story and MAY be helpful to figure out the mastermind or the password you missed.
In General: The passwords from day 10 and later can be solved without watching the bad ending! Just read carefully whenever Dave starts his investigation and write down sus words on your paper.
Path A: Support Benson, solve all Passwords after day 9
Path B: Reveal Oz, solve all Passwords after day 9
Path C: Support Benson but FAIL Password on day 10
Path: D/E: Reveal Oz and FAIL Password on Day 10.