As I noted in the sale article, the delisting of the 'Add-Ons Collection' doesn't mean anything. If you check the dates on Storeparser's graphs, you can see it always gets listed and then delisted for every sale it's been a part of.
I personally still believe the game and the individual DLC will be delisted, just that this particular delising doesn't have any bearing on it.
Edit:
Cookie Kenku said:As far as I know, Complete Add-Ons Collection for Forza Horizon 2 was only available for purchase when on sales and disappeared afterwards till new sales
What they said