I understand the reasons for trying to make the toolbar shorter, but I've had comments from members and I know other forums have too about the 'disappearance' of strikethrough.
Arguably (though it will vary from forum to forum) I'd have thought that indent and outdent, and possibly underline, are used less than strikethrough. I certainly can't recall indent and outdent being used on my forum whereas strikethrough has.
Personally I'd prefer to have one extra button (strikethrough) back and more readily available than having it hidden away.
In the meantime, @Chris D has posted a solution to this which requires the editing of a .js file