Theoretically the Seasons installation don't desinstall any EP but saved games with Seasons cannot be load with a pre-Seasons version of the game.
You have Pets EP who don't function now ? It is the problem ? I'm not sure but it's normal that the game begins now with the Seasons icon and not Pets one.
If you desinstall Seasons you will actually lost all. I hope you have a pre- installation of Seasons save somewhere.