ssl certificate for sub domains

I'm trying to understand if this scenario will work or not- I have a multisite set up with sub domains. My main site is One of my sub domains is The actual domain is which is mapped to the sub domain and I currently have about 20 sites running with this same configuration. I understand that if I purchase a wildcard SSL certificate that all the subdomains can share it. But- When a visitor comes to a site using the actual domain name and not the sub domain it's mapped to will the SSL certificate still be valid?