A possible future. To be honest, I've contemplated over which endgame I'd prefer for these two.
-One end, I think it'd be more true to their characters not to settle down and live freely continuing their paths. Zoro will never stop trying to grow stronger, and Tashigi will always be a woman who's sense of justice compels her to continue doing good.
-On the other, they've matured through their experiences, and it might make them reevaluate and broaden how to carry on their futures. Zoro might find it more rewarding training the next generation, while Tashigi feels cultivating them into upstanding citizens could lead to a brighter future.
It's why I find it appropriate they open a dojo together should they choose to settle down. Or if they don't, be on good terms, and always remember eachother wherever they may be. And should they bump into eachother during their travels, communicate and reminisce about the old days.