[Puke]

I have seen races regain contact after losing all planets. you have to re-establish contact manually, by having mutual line of sight between ships or planets.

if you cant get back to defend your planets, or its strategically unviable - and your 300+ DNs are important to you allies, have them give you a little moon or something, and of course have them keep gifting you enough resources to pay your maintainance. keep in mind that resource storage will be a problem once your planets are gone, so maybe have them give you some storage facilities, or build them as soon as they give you a planet.