Assuming we lose Toby and Eriksen, I think there are a few questions we have to ask first of all.
1) What is Ben Davies? Do we turn him into the left sided centre back that we need and save ourselves the hassle of finding a fourth CB?
No. What we need is a top-class, long-term replacement for Verts - i.e, a left-footed centre-back capable of being as good as he was. I doubt Davies is that player, simply because we would have already tried that more frequently than we have, were that to be the case.
Mario Hermoso, perhaps, if Madrid don't snap him up in the summer.
2) Do we move Dele back to cover the spot that Eriksen is vacating and bring in a new player to fit the tip of the diamond or do we look for a creative CM like Eriksen?
I think it has to be a creative CM. Dele's best role seems like it's off Kane, and once Eriksen leaves, a minimum of disruption to the first team will help keep us ticking over as we cope with the huge loss. Thus, keeping Dele where he is probably makes sense.
I think, if Eriksen leaves, we'll try getting two birds with one stone by replacing both Dembele and Eriksen with a single player - a creative CM who can pass and press like Eriksen does, and carry the ball well enough to be an option to break the press, if required.
There are very few players like that in world football. Piotr Zielinski comes to mind, but there really aren't many others.
Once we get a player like that, we can move him into midfield to rotate with Winks as required. Then, the attacking midfield three can be changed to adapt to this. Alli central, Son wide, and maybe another inside forward like Son on the other side? Lamela/Moura/new player?
3) Winks into Sissoko's spot and a new player at DM or someone better than Sissoko and Winks remaining at DM?
I think DM is actually sorted - between Dier, Sissoko and Skipp, we have enough players in that position. What we need is someone to rotate with Winks in the other CM position. And for that, see above - go big or go home.