Options for ending a workflow triggered by custom button
If you want to try the retURL function, use what is after the retURL= when you click "New Campaign." For example, when I click the Campaigns tab, my URL is appended with "701" and this may be different for you... so my retURL puts "%2F" before the "701" and "%2Fo" after; you should be able to use that same format: retURL=%2Fxxx%2Fo
(This is what I see when I click new campaign)
There are cautions in SF documentation about using retURL in this way as you can end up with sidebar and header within a window that already has sidebar and header. Thus, the custom button behavior I've used is "Display in existing window without sidebar or header". Thus far, there have been no issues.