I'm not aware of anything that analyzes technical difficulty of a passage, but I know that the latest versions of Finale let you flag notes out of the range of various skill levels.
Don't look for "possible/impossible", target the level you want and see if the music is feasible.
Rather than saying "this is unplayable", you want to look at the way music is graded. A piece will be too challenging for a certain level, but might be feasible for certain very advanced players. An example would be extremely long notes in solo work that require circular breathing, or certain fingering patterns you can only do because of the acoustics of the instrument. Some passages that look almost identical (one note changed) could go from "manageable" to "impossible."
At professional levels, it's on the performer.
Especially in percussion, my world, there's a lot of impossible music that's pretty mainstream. I've played "unplayable" music before: Xenakis' Rebonds B has a motif that requires 3 hands, or the finale of Tchaikovsky's Fourth Symphony cymbal parts at certain tempos, but in every situation there's a way to make it work that's accepted by professionals. Often it's a novel technique specifically for that passage, and as more composers write this way, that technique becomes more standard and mainstream. If things REALLY aren't possible, there will be an "approved" way of fudging the music so that it can be played.
But will the music get played?
Some pieces just aren't played because they're too hard. If you need to spend 4000 hours developing a new technique or retooling an instrument for a 5 minute piece, you probably won't bother. There's other cool music out there.
Grading isn't universally agreed upon; if you're writing music frequently, you might want to talk to a publisher to get an idea of how they do grading. I'd also go over to the publisher's websites and look at the previews of scores for different levels to get a broad idea of difficulty. You can find some idea of what is expected for different levels over at bandworld's website.
A google search will turn up lots more results.
TL;dr: Write for a particular level rather than for what might be possible.