That's not true, the concessions would be based on the regulators concerns. It would not matter if Sony are happy or not. The regulators are not really a mediator. The regulators would either decide that the concessions are required or they are not. Any concessions they decide on would not be at risk if Sony are not on board.
Again, AFAIK, concessions are used to ease the merge at regulators eyes. Sometimes are promises, like nvidia tried with the arm merge, but no one believed them, sometimes are signed contract to third party involved, like this case.
As an example there is the recent psa-fca merge in stellantis. PSA had already a joint venture with Toyota for commercial vehicles, which is deeper than the relationship Sony has with Activision. Stellantis offered to maintain the contracts that already existed, and... that's all. Merger approved and the second biggest car manufacturer of Europe was born. Which than became the first in sales in 2021.
PSA has offered to increase production capacity for Toyota at their van joint venture in France, a source told Reuters.
europe.autonews.com
What Microsoft is offering is way beyond that as there is no joint venture and there is only a paid exclusive marketing contract right now.
It must be considered tha automotive is a core industry for EU, and the commercial vehicles busines may had a big impact in a lot of small and big businesses. Videogame are far from that
That said maybe they find out other things to block the deal, but honestly I don't think that what Sony ask for will be determinant. I think the 10 year deal is convenient, and, even if regulators are taking the parts of Sony, more or less clearly, if Sony become greed it may go against themselves.