For once, I actually agree with Gustav. I have no idea why any Roleplayer with half a good rep would walk straight into this, especially with the way you put it - you make it sound like it's guaranteed.
It wouldn't quite work well with realism that much, either. Nanobots simply can't really traverse solar systems in a reasonable amount of time - sure, they can burn the interplanetary hydrogen however that's a method that's inefficient as fuck, and long-range warps will only be possible with a deployment medium, such as a mothership.
Also, some weapons cannot be dodged within a certain range. If the nanites have to get up close, then the enemy will have plenty of time to launch a well-aimed attack.