What does an android Launcher actually do?
A launcher, in simple terms, is an interface for your home screen; it determines the appearance of it, if you like.

If you were to install a 3rd party launcher (Nova is quite common), it would not run on TouchWiz, nor would it uninstall it.

If you do install a new launcher and want to go back to using TouchWiz, it's just a simple matter of tweaking a few settings in the Settings app.