Speak with Chromie a third time, then travel to the future and attempt to save her again.
Attempt to save Chromie
Well, unfortunately for... whomever is fixated on blasting me into oblivion, I am a fairly skilled master of the timeways! We have the advantage of trying that again, and again, and again, until I'm not dead anymore.
We're going to need a little more than a few seconds to stop this attack. How does four hours sound?