Your archive page will still exist, as WordPress generates it automatically. The archive page is still handled by your theme.
WPSP is meant to display short lists of posts on static pages – it’s not really meant as a replacement for the main archives within your theme.
There is a way to replace categories/archives with a static page though – it’s just a little complicated: https://generatepress.com/forums/topic/replace-default-post-category-template-with-a-blank-page-template/#post-608394