With this SQL query you can select all the posts from a specific term (and post type):
SELECT * FROM wp_posts p
LEFT OUTER JOIN wp_term_relationships r ON r.object_id = p.ID
LEFT OUTER JOIN wp_term_taxonomy x ON x.term_taxonomy_id = r.term_taxonomy_id
LEFT OUTER JOIN wp_terms t ON t.term_id = x.term_id
WHERE p.post_status = 'publish' AND p.post_type = 'post' AND t.slug = 'term-slug'
With this query you can delete all these posts:
DELETE a,b,c,d
FROM wp_posts a
LEFT JOIN wp_term_relationships b ON ( a.ID = b.object_id )
LEFT JOIN wp_postmeta c ON ( a.ID = c.post_id )
LEFT JOIN wp_term_taxonomy d ON ( d.term_taxonomy_id = b.term_taxonomy_id )
LEFT JOIN wp_terms e ON ( e.term_id = d.term_id )
WHERE e.term_id = <term id>