You can definitely play a pianola manually. I don't think the Pianola Museum had an example of one that couldn't, although I may have missed something there, as the technology went through a few changes (the first ones were an entirely separate piece of machinery that you wheeled up to your ordinary piano until its hammers touched your keyboard).

There are apparently many pianolas out there which are now just pianos, the mechanism having stopped working or been removed. I spotted one in a pub a few years ago - the landlord had no idea! Most of the mechanism was there but I suspect it wouldn't be a simple job to restore.