It is important to take regular back-ups of your template and blog-content, to avoid circumstances like these:
Example 1 - Template lost
Example 2 - Comments deleted
Example 3 - Blog banned and marked as spam
Official word from Blogger: Mistakes do happen.
So, precaution is aLwAyS BeTTer than Cure !!!
1. Tutorial for blog posts and comments backup.
2. Tutorial for template and widgets backup (read the first 6 steps of the tutorial).