I am hopeful that there are good negotiators in the club = e.g. Brands and Silva = who can pitch the idea of staying to him and some of our others big assets. Going to a PL top 6 or CL club is not what it is cut out to be, unless you are going to a stable management or one with a long-term plan. I would say for your career, the only guaranteed progress from Everton now seems to be Spurs, maybe Arsenal in the PL. Man City has a massive squad and a ruthless manager, Chelsea, Man U are not quite stable yet, and you can't move from Everton to Liverpool. PSG, Real and others work according to the whims of the owners and latest manager. So basically, Gueye might have one great season at a CL club, but then what? As opposed to that, we would happily keep him with us for the next 3 seasons as first choice, as long as he plays as well as he has done.
Barkley, Drinkwater, Mahrez, Stones, Lukaku, Coutinho, Emre Can, in fact Mina Gomes and Digne, are all recent examples off the top of my head that 'graduating' to a top club does not mean you'll automatically get the dream of CL football that you wanted. You might not be a great fit, and you might be totally at the mercy to the likes and dislikes of the latest manager.
I hope we can keep hold of young players like Lookman, and the established first teasers like Gueye, Digne, Richarlison on the basis that they can fulfil regular playing and international ambitions because they're at a club that values them with a long-term strategy.