Sometimes it happens that, by the time I am done with my editing someone else have done it already. Hence my change can't be committed. From there on, it's not possible to return to the question without pressing Back button on Browser. This is both inconvenient and erroneous as depending on browser settings, I may see the old unedited post. It would be helpful to have such a link.
When you decide to edit a question, since the 'edit' option is a link, you can open it in a new tab itself via the middle mouse button or ctrl+click (as YOU suggested for the back button), depending on whether you've changed browser tab options.
The benefit of this is that it will work in IE as well (IE < 7 doesn't support tabbing, however), since it relies on use of link characteristics, rather than browser supported back functionality.
When you are notified of an existing edit, you need only refresh the other tab to get the latest version of the question/answer you were editing, which also solves your problem with seeing an old version from the use of the back button.
If you are editing and you need to return to the question, you can simply click cancel or Esc to revert the edit - or use the existing question link at the top of every question (On the title).
cancel link has been added to the edit page, to mimic the behaviour of the inline-edit functionality. This link functions as per your request.
Of course, with the inline editing, you might just edit it inline and click
cancel if there is a problem.
You could just click "Back" button while holding down Ctrl key also. (at least on Firefox and Google Chrome)