Why your website is not expendable to your business.
Your website is your information hub for everything related to your business. Facebook, Twitter..ect are the channels which help bring your audience to your information through your website. Put the two together and you have a symbiotic relationship between your website and social media, with social media being expendable.
Think of it this way, we have seen social media platforms emerge and collapse within the past 10-15 years. Although one would hope Facebook, Twitter, Instagram..ect..ect would not meet similar ends, lets say they do. What will happen to your content and audience? Your content and audience will disappear.
This is why your social media platforms are expendable and your website is not.