not every civilization in the Cosmos needs to have suffered a Fall, therefore there's no need to assume that "salvation" (whatever that really is) is needed outside of humanity. C. S. Lewis's Perelandra posits that Venus is threatened with something analogous to the original temptation and Fall, but protagonist Ransom is sent to help prevent it, and hence Venus completely avoids the need for Jesusy redemption.
and I rather hate that I can summon up this line of rationalization from decades past. I haven't read Perelandra in ages. in any case I would guess most hardcore Christians these days find it easier to pretend that humanity is the only sapient life in the Universe.
~Chara