Uninstallation Question

Make sure you copy your TS2 folder to a safe place. Then if anything does go awry, you've still got your SimsWorld the way it is now.

Neighborhoods. With Seasons as your latest EP, your current neighborhoods will be unplayable anyway if you uninstall Seasons.

Houses. You could try exporting the houses to import back once Seasons is gone, but I don't think it will work.

CC. Any CC that requires University or Seasons will not work. As horrible as Uni is for gameplay, it brought numerous meshes that have been recolored and modified, opening up the custom furniture business and to a lessor extent, custom clothing.

Families. Families and Sims occupying the Seasons based neighborhoods would be deleted along with those neighborhoods. You could export the sims with the houses, but if the houses can't be imported back into a non-seasons game as is my experience, you'll still lose them. So any sims you want to save would have to be exported via SimPE. Once they are brought back into your game, skills, relationships, friendships, jobs, memories, etc will all be gone, just as a sim coming out of CAS would be. Mods such as InSIM could fix most of those issues though.

Bottom line is current neighborhoods would be deleted along with occupying houses, families and sims. With planning and work everything could be recreated, but probably with more effort than it's worth, although Sims themselves can be saved via SimPE. You have to potential of losing CC, not to mention broken mods that would have to be tracked down.

Good luck!