Can I default My Multisite to the main "root" multisite when the address entered does not

I couldn't figure out how to even put this question into a Google search, so I thought I would come here and ask. The scenario is as follows. I have built a multisite for the wife's home party plan business. So, she has consultants who sign up and they get their own subsite for marketing for which they pay $12 a month for. Obviously, some consultants will drop out. At the moment, if you go to a sub-site that does not exist, it goes to [root]/marketing-center?action=new_blog. No idea where THAT comes from. I would like to option the system so that if a consultant bows out and that sub site is taken down, but someone tries to go that subsite, it redirects to the http://root. Hope that makes sense. Thanks!