The way I see it, he is an extremely wealthy man already.
And I am talking about a "mutual consent" type of thing whereby if he did reach an agreement with the club next summer, they would probably split the difference and he is "only"

Blink

forgoing £3 million.
Which I would imagine is a price Koeman would consider worth paying so as not to have a sacking to his name.
But this is all idle speculation of course
I think one thing we agree on is he ain't for sticking around here beyond the three years and that in itself not a great motivating factor for him IMO nor a satisfactory situation for us.
I would much prefer I felt our manage was anxious to stick around for a longer time and was desirous of a contract extension and was striving to prove himself worthy of one.