The new product launch we had all worked so hard for was a disappointment.
So if we removed that we would have:
The new product launch was a disappointment.
But what new product launch? There's a lot of new product launches out there but we're talking about the one that we had all worked so hard for. This makes it a defining relative clause because it's essential to understanding the sentence properly.
If the sentence said:
Our company's new product launch, which we had all worked so hard for, was a disappointment.
Then if we removed our relative clause we would get:
Our company's new product launch was a disappointment.
Now we still understand which new product launch (our company's) this is a non-defining relative cause because it's giving us additional information that is not essential to the sentence.