If you back-up all the files in the "The Sims 2" folder where you find your Downloads folder, then reinstall (in the correct order), then replace the generated files with your backup, things should work fine.
I installed the game on my new computer (first the EPs and SPs I used on my laptop), then moved the game from my laptop, and installed the rest of the EPs and SPs, and everything was on place, nothing deleted or disappeared.
That's why you always should take backups before installing a new EP or SP, you know