This is something that i search for a long time. I want to delete dates from my pemalinks structure without affecting search index.

Let me explain this using hongkiat post :

You want to remove particular prefix (Dates, for example) in the URL on all your permalinks but you can’t bear the cost as your entries are either indexed by Google, hyperlinked by bloggers or bookmarked by other websites.

(a) http://www.domain.com/blog/2007/01/11/name/ (no good)
(b) http://www.domain.com/blog/name/ (good)

Read full post: Change Wordpress Permalinks without affecting search index.