UPDATE: If you are using the new Blogger dashboard, read : "How to Back up your template and widgets here".
If you blog via Blogger , it is always advisable that you Back Up your template before making any changes to "EDIT HTML" under the template tab. More so, you should always Back Up your blog widgets before changing your Blogger template.
Backing up your template makes it possible for you to restore the template should in case the changes you wish to effect to the template code ain't successful thereafter.
More so, you must always back up your BLOG WIDGETS or else you will not see them on your blog after changing your template. Your blog widgets are the stuffs you add to your blog e.g Feeburner EMail Subscription box, Facebook badge, Search box etc
I hope this info helps...
If you have any question to ask or have contributions to make, kindly make use of the comment form.