It's certainly more likely than a site with no users.
Because it drives multiples of traffic?
Which is mostly unmonetisable by anyone other than advertising more porn. So it's not worth that much?
Except from what everyone is saying and the drop in traffic people are observing it drove multiples of SFW traffic. The porn kept and drove users but they also viewed plenty of SFW content as well. You can monetize the SFW side of things.
As far as I know, Tumblr has never come close to being a sustainable, profitable business; it survived on VC funding until it was bought by Yahoo.