[dragonwriter]

> Article 5 doesn't apply if you send your soldiers on some mission (e.g. defending Finland) on your own accord and Russia kills them.

That depends where you send them, as Article 5 has geographical constraints specified in Article 6 (there is no general exceptions for troops being attacked after being voluntarily sent “somewhere”.)

Moreover, even without triggering Article 5, an attack on NATO member troops in the Euro-Atlantic region but outside the territory specified in Article 6 would probably be a trigger for regional security consultations under Article 4, which have produced more NATO interventions than Article 5.