(a) quite true. And as mentioned before, he's expensive. What Cumulus is doing is a simple cost analysis. An expensive investment isn't a problem--- IF you're getting return.
(b) it's not clear if they'll replace talk with talk (and they have their own talkers so the cost plummets in that move) or if they're assessing talk radio in general. The fact is the demographic of old angry white geezers is dying off, and any business analysis, especially one dependent on a public audience, has to take that seriously into account.
To B – I was not insinuating that was not a possibility. Even if that happens though, the impact will be rather small. What I was saying is that the audience is there (even if smaller) and they will simply go to another station or venue as in the case of XM. In the grand scheme of things, it is almost irrelevant.
Really, it would not surprise me that much of that audience is FINALLY moving to the internet anyway. The same ditto heads are opening attractions there as well (the Blaze would be good example there). Even if the venue changes, the market is there and will always be there.
The OP makes this out as some sort of victory for liberal thought but in reality it is far from that. It simply represents changing ditto heads and demographics.