First, only tce extensions are taken into account by the uninstaller. Tcz is left alone. Let's take glib2 for example. Say it is dependent on expat2.tcel (it is not but for this illustration). Assuming none of it's files are in use by other apps, use the uninstaller to try to uninstall it. What you will see is a list of installed apps that depend on glib2 - on my box now it is atk, emelfm2, gqview2, gtk2, leafpad, and pango. Three options are then presented:
1. Do not uninstall glib2 (recommended)
2. Uninstall only glib2 (for advanced users only).
3. Uninstall glib2 and those that depend on it.
Dependent apps are offered up for uninstall, not dependencies. Expat2.tcel would be left alone. It wouldn't be good to uninstall dependencies "below" an extension, but it is good to let the user know of the dependent apps "above" it so they won't get broken. Of course, if a .dep file is incomplete, then breakage is possible somewhere. But that would be a case of a broken dep file rather than a broken uninstaller.
I hope this clears it up a little. Sorry my response earlier was snippity.