I really can't see PSG not coming in for him if Mbappe leaves. Leonardo loves him and frankly he's better for Poch's system than any of that front three in terms of work rate (if Poch is still there mind). Obviously the Neymar factor too (not to mention Messi).
On the other hand, if for whatever reason Mbappe doesn't leave to Madrid, then I equally wouldn't be surprised to see those go for him. Again, assuming Ancelotti is still there (who knows on that), then that's a big pull. Richarlison loved playing for Carlo. Whether we think he regressed or not, they really rate each other. But if they don't get Mbappe, I think they'd want a bigger statement signing like Haaland (though I'd find it mad if City aren't all over him, depending if anything happens with Kane in January)