I'm not sure I can see Vertonghen going anywhere tbh. Here's the facts as I see it:
1) We have Levy. Levy will value Vertonghen at £30m minimum, no question, and it's a snip compared to Luiz.
2) Clubs don't like buying from spurs because of Levy, as above.
3) Barca had to sell Sanchez to justify/afford (probably the former) buying Suarez. That left then around £30-£40m out of pocket, too. Can they really afford to spend that much on Vertonghen who, while he had a good WC, isn't at his peak form in general.
The problem is if Vertonghen wants to leave and Levy holds out on the best deal for the club, if we retain him then what player will we be keeping?
He didn't seem too happy under either manager, so it'd be a lot of pressure on Pochettino to keep him on form and in good spirits. If we start the season strongly, this might not be an issue, but if we start poorly then it could turn out quite sour - especially if the window is still open at that point.