In theory, Stardew Valley could go on forever. However, it gets to a stage where there’s very little left to achieve and so, fun aside, no point in carrying on. I’m not quite where I would want to stop playing just yet, but I do feel that after 120 hours (count ’em) it’s finished.
I’ve achieved most of the achievements, unlocked Qi’s casino, shipped every item, got married (to Emily), finished the Community Centre, broken into the witch’s house for the wizard, unlocked the sewer, reached the bottom of the mine, made (in total) over 4 million gold, reached level 10 in all the stats, and maximised my relationship with almost everyone[ref] bar Elliot and Sebastian – Elliot won’t talk to me, Sebastian is a misery[/ref].
So yeah, it’s completed.
Until they release the two player mode update, and then I’m back in, I expect.