Would it though? The expansion speed would even at Clarketech level advancement, be more than a few hundred years. And we've only had telescopes capable of seeing this and the idea of what to look for, for a very short time in the scheme of things. For all we know it is happening just we haven't seen it yet, and also let's not forget that if it's hundreds, thousands if not millions of light years away it would take just as many years for the advancing darkness to reach us. The fact we haven't observed it in the last 50 years does NOT mean it's not happened. Doesn't mean it has either but the argument that "because we are capable of viewing light from up to a billion light years away and we haven't seen it, it's unlikely to exist" is flawed.