Adieu. Aufwiedersehen. Gesundheit. Farewell.

[Merlin]

I would think a middle ground should be met. Her individual posts should be removed (or replaced with deleted by author would be better) with the main thread/link still available for SEO purposes.

An SEO campaign that links to a thread wherein the relevant results have been "deleted by author" would lose their SEO rankings pretty quickly, as SEO algorithms specifically look for relevant content on landing pages. Not to mention, that's not really the issue here. Based on the discussion here, the forum admin/mods and community seem more concerned about impact to the community/community knowledge-base in this situation, not the digital marketing impact of SEO consequences.

I took it from the site administrator that the issue was broken links within search results.

Broken links or links that redirected viewers to empty posts since the content of the original post had been removed. This caused confusion for visitors in addition to looking bad.