VACUUM ISP. I really don't know at this point if you're trolling on purpose or if you've been simply cognitively challenged since birth. 334 s is a sea-level figure that has nothing to do with my claim about VACUUM ISP.
Yeah, it's true...the things that bite you are the things you don't anticipate. On the N-1, they only found in a test flight that shutting down six engines at once to limit the g-forces creates a hydraulic shock that ruptures the fuel lines. Well, that's too late to find out about something like that!
You can't really make such assessments without a more comprehensive model. The engine-out capability depends even on such things as when the engines fail (later is better than earlier) so it's not something you can assess just by exponentiating one engine's reliability by its count.
Even if terraforming it takes a few thousands of years, it will stay habitable for at least two orders of magnitude longer. And I'm not sure anyone cares what will happen even 100 ky from now since who knows what capability mankind will have at that time.