Even if some subreddits choose to extend the time period (even indefinitely) Reddit has no reason to really care - most of them are so small they don't 'move the needle'.
I appreciate that the decision Reddit is making and their justification both seem poor. But the response seems like people are missing where and how Reddit makes its money.
None of those threads received any non-joke replies.
The only thing that will make Reddit change course is serious competition. Probably not even that, since as long as the exodus happens after the IPO, it's the public that will be left holding the bag and not the investors.
The vast majority, 99%+ just use the site casually and don't follow any of this drama. They will use the site regardless of what goes on.
Even among those who are disgruntled, many of them will just come back to Reddit anyways, because it's large enough that it has a huge chunk of content that those alternative simply don't have.