Magento – How to check if a product exists in catalog, rather than deleted, when on Order View page

Ok, so I've learned how to make the product name a clickable link (when viewing an order as admin) to that product's Edit Page on our Admin Dashboard – here's the post w/ answer.

The answer shows this is the code to add to:

app/design/adminhtml/default/default/template/sales/order/view/items/renderer/default.phtml

<div class="item-text">
<?php $_pullProduct = Mage::getModel('catalog/product')->loadByAttribute('sku', $_item->getData('sku')); ?>
<a target="_blank" rel="external" href="<?php echo Mage::helper('adminhtml')->getUrl('adminhtml/catalog_product/edit', array('id' => $_pullProduct->getId()))?>">
<?php echo $this->getColumnHtml($_item, 'name') ?></a>
</div>

This works perfectly, except for one thing: If the order has a product that has been deleted, that snippet of code that gets the product URL can't find the product, since it's been deleted, and the HTML stops loading at that line, breaking the Order View page for that order.

Orders with products that have not been deleted work fine with this bit of code.

How might I go about only linking to the product URL if the product exists in the product catalog and has not been deleted?

Btw, These products are deleted forever, rather than simply disabled. Disabled products work fine.

Edit/Update:

Thanks for the answers – Both look great, and I believe Fabian's answer was closer to was I was looking for – Here's a question for Fabian's answer, which I attempted to ask in the comment form, and didn't look too good, so I shall ask in a more readable way here:

I'm having a problem figuring out how to implement your answer and is most likely because I'm slowly learning PHP, but I'm not too experience with it since my main job is design, but I do manage to get by with the bit of PHP I've needed to learn. I attempted:

using…

if(!$product->isObjectNew()): do something

and I ended up trying…

<div class="item-text">
    <?php echo $this->getColumnHtml($_item, 'name') ?>
        <?php if(!$product->isObjectNew()): ?>
            <?php $_pullProduct = Mage::getModel('catalog/product')->loadByAttribute('sku', $_item->getData('sku')); ?><a target="_blank" rel="external" href="<?php echo Mage::helper('adminhtml')->getUrl('adminhtml/catalog_product/edit', array('id' => $_pullProduct->getId()))?>">View</a>
        <?php endif; ?>
</div>

…and this does not work, and I understand it's because I'm incorporating:

if(!$product->isObjectNew()): do something

improperly.

I'm not sure what my flaw is, even after looking at similar code in other phtml files on the site, attempting to copy what I see, and I'm still unable to figure this out. This is where I could use help from you guys, this would be a great opportunity for me to learn something.