There is an easy solution. If Google Chrome says the certificate is invalid, all they have to do is "add an exception" and then they can access the site. It will still use https and be encrypted. The only purpose of an SSL certificate is to basically say "this site is legitimate" but in a work/business environment I would think people would know where they are going and if it's safe (hopefully). Additionally, having a certificate doesn't necessarily even mean the site is safe. Your data can still be compromised. I have acquired a certificate (I think it was from Comodo) for my website before, and I have to say they have absolutely no idea what I can do with my website even though I have said certificate saying it is safe.
SSL certificates have always been somewhat of a money grab IMO. It doesn't actually change the connection or encryption. It's more of a business gimmick of "give us money and we'll give you a certificate saying your site is safe and friendly". It gets even more crazy, if you want your website to have that "green lock" in the URL address bar of your web browser, you have to pay a ton of money to the certificate company, I'm talking like over $100,000 from what I recall. Big corporations like microsoft.com will have this.
TLDR certificates are a money grab that don't really changer the connection at all. They're supposed to mean a site is legit and safe but undoubtedly an unsafe site can surely get a certificate. Idealistically the certificate companies should be looking at the sites that have their certificates to ensure the safety, but I don't think that happens.