"I never miss the bus!"
Translation:Jag missar aldrig bussen!
why can't I use "saknar" in stead of "missar" (both are given in the hints)
Would it be totally wrong to put aldrig at the end, just a little odd, or perfectly fine?
No, because the verb must be in second place in the sentence (the V2 rule).
It's grammatical but very unidiomatic. You'll likely never encounter it outside of e.g. poetry and lyrics.