#2 Might help in retaining other players

According to a recent report, Spurs have a wage structure in which the maximum a player can be paid is £110,000 per week and considering the astronomical wages that other clubs are paying, it is unsustainable.
Kyle Walker walked out last year and Toby Alderweireld is on his way out as well after the club refused to give in to his wage demands of £150,000 per week.
Needless to say, this simply means that Spurs will continue to lose players if they do not do something about the wage structure. If players keep leaving, then having Kane in the squad is of no consequence. Even he will leave if the team keeps getting weaker every year.
In that regard, his sale could actually turn out to be the club's salvation. The huge transfer fee may help them in raising the wage bill somewhat and pay some of the key players like Eriksen, Dele Alli, Alderweireld, and Jan Vertonghen a competitive wage.
The sale might give the club the finances to keep the rest of the squad together
In a twisted way, perhaps, Kane's sale could probably help Spurs in getting stronger than they ever were as football is a team game after all.