Based on his offensive point totals, the starting point is $8 million
Deduct from that the fact that Kessel is a defensive liability and soft as butter and the figure you should arrive at is about $6-7 million.
$8M (PP production and ES offensive production)
$1.5M (No PK contribution and minimal effort ES defensively)
$6.5M (average long-term cap hit)
When people make costly mistakes in the workplace, they either have to fix it, pay it back to the company, or leave.
Since we can't assume Kessel will ever put in a good effort in playing two-way hockey seeing as he hasn't done it for his entire career, and since we don't really want him to leave, he will have to pay back the Leafs for his ineffective and most times non-existant two-way game.
What's fair is fair.