How to properly remove Discourse forum from subdomain and internet

First, I want to say that I love Discourse, but the forum I have didn’t really took off, so I want to know what’s the best wait to remove it from the internet.

The reason I’m asking is that the forum I have is a subdomain for the main website, so I want to make sure that anything I do won’t affect the SEO of the main site or Google.

Can someone give me an overview on how to go removing the forum? Do I have to deal with redirects? Will simply removing the forum will cause Google search problems with the main site? etc.