There is always a risk in everything that we do. I have had number of cases where freely/editorially published pieces by staff writers were removed without any notice.That's always the risk if you pay for content to be posted I guess - it'll be against the site's T&C's so if they identify it, they'll remove it.
Pretty much every small or big news/content site take sponsored content, where clients have to pay hefty prices to sites directly, this is part of PR and digital marketing ecosystem. I only take sites that are somehow relevant to the target site and can add value. Every article that is written is reviewed by site editors/owners and only gets published if it passes their editorial standards and they believe the content and links add value.
There are number of clients who I refuse to write for because their sites do not fit right with the target site, and in rare cases when links are removed I provide with an alternate solution.