I don't think the expression "genocide-chic" implies that everything must be dark forevermore, merely that it is currently trendy to have extremely high body counts as a show of "grittiness" or "credibility" or whatever. This is not an expression I personally employ, but I understand the trend it is attempting to define.
As for life going on after a tragedy, naturally it does, but I do think an absolutely unprecedented catastrophe on the scale of Destiny would have a profound impact on the Federation, more profound than it is likely to have in the follow-up stories, where I don't expect much will change other than a few planets will be missing., a few shifted alliances, that sort of thing. This is similar to Vulcan being destroyed in Trek '09: there's only a handful of Vulcan characters that we care about, so essentially everything else is disposable. Not that I have a big problem with that either. I mean blow it up if you feel like it, whatever, it's entertainment. It's a trend like any other, and of course not even a particularly new one.
Basically, my reaction is something along these lines: if you are going to kill billions in an unprecedented disaster, there should be some serious and far-reaching consquences, otherwise it feels empty (this is where "genocide-chic" comes in: it just feels like fashionable window-dressing); or alternately, don't bother with the body count at all and just tell a different story. Dark is fine, if you're really ready to go there. Not dark is also fine, and perhaps more suitable for the Trek universe. But "disposable darkness" is less palatable to me personally.
Naturally all this is contigent on what eventually happens in Typhon Pact and so on. Frankly, it's been ten years or more since some of these shows have even been on the air, so I'll take what I can get
