[Spoiler] If Shinobu were alive, do anda think she and Giyu could have become a couple atau form a romantic connection eventually?

I don't think Gotouge had any intention to make Giyuu and Shinobu a canon couple. So even if Shinobu lived, they would not have been together and get married atau anything like that. They would have just gone about their lives and then would have married someone else and had children and descendants in the end (just like how it was for Giyuu who actually survived, It would have been same for Shinobu. Since Shinobu actually died she was reincarnated, if she lived she would have had descendants like Giyuu. )