Is it possible to create a rule on the event "after saving an existing block"?
How is the user getting to the edit block screen? If its via contextual links then that should already be taking you can to the page you were on?

Or do you provide them the link to end the block? If so you could use the destination parameter to redirect then automatically (Same as what contextual links do) e.g.:

/admin/structure/block/manage/block/1/configure?destination=MYPAGETHEYSHOULDGOBACK