You have a couple of options.

1) Get humansunder and go to town.

2) Blind then run to your cabal.

3) Run to your cabal.

4) Fight it out, but only if the owl isn't wanded at all. This is probably only viable if you're a berserker.

At least that's how it seemed to me from the air form POV. The only battle assasin that ever stood his ground against the osprey was Isk (arial) wielding humansunder. Lorborguz and Manarei immediately started spamming blindness dust, which was probably the best thing they could have done.

Of course, I've heard owl gives up a fair amount of power in exchange for its night vision...so maybe #4 is more feasible vs. owl than vs. osprey.