This posting is very true, and this is exactly why I prefer Free Software when it comes to sustainability.

Even if the developers' revenue plan (services, merchandising, whatever) turns out to not be sustainable, at least the remaining software is free (in the sense of freedom) such that others can fork it and can take care of it.

In that sense, Sparrow could have made a great move, since they don't plan to make any more money with their product: publishing their latest code base under GPL.

However, in that case Google might have hesitated to acquire them in the first place. On the other hand, MySQL has been acquired by Oracle despite being Free Software, and despite having existing forks such as MariaDB.