I think at this stage we have to assume he's not coming back. Obviously it'll be a huge bonus if he does, but we need to build the team around the assumption that Kompany won't be available. Stones is a talented young player, but let's make no mistake, he was our third choice in the summer after Bonucci and Laporte. He was never intended to come in and turn our defence into a rock solid unit by himself. He's a kid who needs to be playing alongside a world class centre back to learn, but we only have one of those, and he's constantly injured. And they're not exactly easy to find. Tbh, I'm trying to think of a single one in the Premier League other than Kompany. Terry back in the day of course. Alderweireld, possibly?
Personally, I'd be all over Van Dijk, but given how much we've spent on CBs recently, I can see why they'd be reluctant to try and put it right by throwing yet more money at the problem, especially for someone who's not proven world class.