I think you may be overestimating the complexity of hardening. It's something we do very well. Consider Hubble, manned missions, and also the probes that have journeyed much farther out than Earth's orbit. Hard to imagine that simply upping the image resolution would pose a major hurdle in that arena.

BTW, the solar panels upon which Rosetta relied to make the journey were pretty cutting edge. And Rosetta is the first mission to go beyond the asteroid belt relying only on solar power.

Had they failed, the entire mission would have failed.