You can uninstall by choosing package yes.
When you uninstall Seblod you will be left with some codes in the articles and no content. Also all menus pointing to list/search types, forms etc that lead to seblod directly will be dead (404), you will need to recreate them using joomla com_content views (e.g. category blog).
There is unfortunatelly no tool to convert seblod articles to joomla ones, easiest way probably is to make a copy of the site, uninstall seblod on the copy, then create new article for each article you wish to transfer and copy content from original one by one.