From my understanding, Spurs told their sources about the £25m fee, which is the upfront payment, since typically fans will take the first fee and quote it everywhere. It's a successful tactic and it's technically not lying, it just misses out the £10m add-ons that were later reported by Sky, Naylor etc.
Bissouma was replaced 18 months ago, little fella called Caicedo. He was expected to go last summer but it ended up not happening, so the replacement played alongside him. Bissouma is nowhere near as big a loss as Cucurella would be, so if he does go I expect immediate re-investment.
The Brighton model of signing foreign, unknown talent and hoping that at least some of them blossom into top players has worked out very well, as long as Brighton remain a solid Prem team I don't see a reason to shift to a model that only the top teams can really pull off where they pay big fees for established players.