Mercedes and Wolff have been telling everyone how good of a relationship their drivers have but I wonder how much Vettel and Kimi's relationship could affect this decision. It was a well known fact that Vettel and Kimi got along nicely even before neither of them were at Ferrari but I don't know how their relationship is today. Ferrari seems to he going with clear #1 and #2 drivers and Kimi hasn't been much against it. He knows what his role is at this point and doesn't try to fight against it. For example in Hungary he said he had pace to continue but still decided to box as the team told him to. I'd guess if he said "sorry I'm staying out" and took the victory from Vettel he wouldn't be getting this contract.
Guys like Perez and Grosjean who are just some of the names looking for that seat would probably never do that. Usually the team values construction championship more but is that really the case for Ferrari? They definitely don't have trouble in money since they are getting paid simply because they are Ferrari. Also a driver world champion is better promotion to the brand than the construction title would be.
That being said I'm confident the Iceman will take another victory home at some point either this season or the next. Everything's bound to get together some race. He could've easily taken the victory in Monaco and/or Hungary already. Why not next weekend already, he isn't called the King of Spa without a reason.
Although Mercedes fits the track better than Ferrari. We'll see.