Buying an old domain

If I buy a domain that is expiring soon and revamp the site under the same niche will the existing backlinks still work? Sorry for noob questions

Has the owner disavowed anything?

Yes it will!

It looks to me like the owner has ZERO knowledge of SEO, webmaster or anything else for that matter. I'm unsure about the owner having used disavow but from the looks of things, web design, branding, SEO etc etc it would appear to me that they paid somebody a one off payment to build this site and just left it alone.

The site has one month left and I'd love to buy this domain. I'd hazard a guess that the owner isn't even aware that the site is offline but I can't buy it just yet! Any tips on securing this domain?

Yes they should work.