'The Sims' (genre/franchise) is a life-simulator that is clearly loved by millions (yes, millions) around the world. Having said that - 'The Sims' (genre/franchise) seems to be changing its routes from an (open-world) life-sim' to a more character-focused sim', as I've read and heard. Although 'Maxis' claimed they'd only make a 'The Sims 5' if 'The Sims 4' sell good; I think they will make a '5'. The game has its popularity among the masses of gamers who like to play it, so, needless to say, I think they franchise will definitely continue.
To conclude:
I reckon there will be another installment, because I reckon '4' will sell good enough for 'Maxis' to consider making another 'The Sims' game.