Yes. But it's not as easy as deleting them because you need to know the name of the panel. For example, if you were to delete the Category menu from your home page and then you decided you wanted it back, you'd want to add back the panel called "SideCategoryList". Here's how you do it:
1) Enter into Design View for the page you want to add back a panel to.
2) Right-click somewhere in the white space on the page and then select Edit Layout.
3) In our example we want to add the Category menu back to the left side of the page, so we're going to add it back to <div class="Left" id="LayoutColumn1">. Directly below that line, we're going to add:
%%Panel.SideCategoryList%%
4) Now we click Save in the top left side and refresh our page. Our menu is back!
You can scroll down the list of "Other Template Files and see all of the other panels. The ones that go on the left or right side start with Side, naturally. The rest are pretty easy to figure out thanks to Interspire's naming convention policies.

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