Well, I have checked again as you recommend, and still canīt find the gallery app.
Also I enabled G+, but the icon Gallery is still missing...
But! always there is a But... I checked the G+ Photo Gallery, and looks pretty similar... is not the same, but very similar.
And in that moment, I remembered with gallery, there was some config to upload / syncronize with G+
So probably the G+ has changed, Or when I disabled G+ something stop and never came back again.
Some things are a mistery too. Maybe this is one of them.