Sudden growth with bad timing

Hey Guys, I wrote a few android puzzle games a few years ago and they did OK, but nothing really impressive. Since then I've moved on to new and more interesting projects but lately one of my apps is taking off without me doing anything, it more than tripled the number of daily installs in the last month and I haven't updated that app in years. That's great, but I don't really feel like managing it right now, as I said I've moved on. I'm not sure why it's growing lately, maybe some kind of app store SEO is finally having an effect, it's a rubiks cube app so presumably lots of people search for that. Is it worth trying to sell it on something like flippa? How much could I expect for something like this? The app is at about $140 MRR at the moment, which isn't much but if it keeps growing like this... Or would it be better just to do nothing, let the profit keep increasing by itself?