They can be forcefully re-opened at any time. Based on the internal memo, they don't appear to be taking this seriously enough to warrant that kind of action.
Harm to the brand is hard to quantify. We can only assume they've done the calculus and decided freezing out 3rd party apps is worth the benefit. Knowing exactly what that benefit is, is conjecture. Best guess is that this is regarding the IPO which is expected in 2nd half of this year.
As a side note: the brand is clearly on their mind, as they've made exceptions for disability features. Banning Redreader would have caused quite a bit more uproar.
