If I'm not mistaken, a large part of Ukraine's industrial base was situated in that part of the country that is now under Russian control.
No they aren't. Things like Kharkov tank plant, lvov tank plant, Arsenal and Luch design bureau, Radionix, Yangel, Iskra, Motorsich are still within Ukrainian controlled territory as well as Antonov. They are of course got knocked by cruise missiles and Geran but they're still there.
What Russia took so far are Donetsk and Lugansk as well as that landbridge, which provided the raw and refined materials (e.g ex Azovstal plant, this provided steel) and logistics to those industries. If they also intend to take the design bureaus etc.. they have to return to Kharkov and shoot their way until Kiev.