If Rosetta crashed but remained operational enough to keep an open connection but not enough to receive commands to close it, it would use up incredibly valuable resources on a highly resource-constrained network.
I don't really understand that. DSN antennas are highly directional because they have to be. If they don't aim directly at the asteroid -- and we're talking a tiny fraction of a degree of beamwidth -- they won't hear anything, even if they want to.
There is no conceivable risk of "jamming" the DSN.
I suppose it's not about "jamming" but rather "accidental overlap" with future trajectories, i.e. another mission may pass through the axis between DSN-station and comet and the signals will mix.
Be aware that the beam is conical, so even if the pointing is exact within a few fractions of a degree, the further away you are from the DSN-station, the wider is the coverage area of the beam (and the lesser the signal strength, of course).
