Would "Non Lapsus" be a good way of writing "Not Fallen" in Latin?
(Lapsus chosen because it refers to the Biblical Fall of Man)
Lapsus seems like a good translation for "fallen"; it just needs to be declined for the right gender and number (one man is lapsus, one woman is lapsa, and so on).
The obvious way to invert an participial adjective in Latin is the in- prefix; unfortunately, in this case, illapsus has its own meaning already. So your non lapsus is the best alternative I can think of.
"The Fall of Man"? Well, if yourself is seeking doom-laden imagery, how about "(non) occasus"?
This masculine noun (gen. occasus), verb: occido, occidi, occasum , as well as "falling" incorporates the "setting-sun"--used by writers to project endings (good or bad); "end" in its own right; and, of course, "death"!
It also means "west". Given the state of the Western-World, at the moment (Brexit to the rise of fascism) there's plenty of (potential) "doom" in the air. But, guessing that contemporary politics is beyond the remit of your Q?
Remember Private Fraser in "Dad's Army"? "We're doomed!" Let's hope not.