I don't think of "die trying," that way, Clive. (Of course, while I have heard of 50 Cent, I am not familiar with his oeuvre.) I can imagine using it in a facetious, almost light-hearted way to express strong determination: "I am going to pull every last piece of nutgrass in this flowerbed, or die trying."
And while "get a life" may be positive advice, I've never heard it used as anything but a mild ribbing at the least, an insult at the worst.
The easiest way for me to imagine this combination is if the speaker is referring to himself. "Another Saturday night, and I'm sitting on my ass on this crummy futon, watching television and eating junk food---alone! I swear to God, in 2008 I'm going to get a life, or die trying!"