This happens on all airlines all the time. This isn't to say that it's right or that your situation was handled well, but honestly, bad stuff happens when you travel and you just have to roll with the punches and prepare yourself as best as you can. For instance, carrying important documents with you instead of checking them in is what most elite business travelers do all the time.
Also, if the FA guarantees your luggage will make it, he/she is probably under the assumption (as they have been informed such) that your luggage will be on the next flight. If that flight is delayed/canceled due to weather related issues, that's not something the FA can really control. Again, not to say what happened to you was right, but you're making it as if the DL employee spat in your face and stomped on your family honor when it sounds like up until the point that flight got canceled, your luggage would have made it just fine.
In the end, the question becomes, did you get your luggage eventually and did your coworker also make it? If the answer is yes and yes, then that's great. Call Delta and tell them your ordeal and demand some type of compensation for both inconveniences. However, realize that if the airlines did get you your luggage, they are not really legally liable for the delay. And if the reason why your coworker was stranded was because of weather related issues, then again, they are not liable.
Finally, you will only get so far with CSRs with a bad attitude. If your mom or you are screaming at client facing agents demanding this or that, they'll most likely not offer you anything - especially if they are not legally liable for any type of damages. On the other hand, if you're really nice, thank the CSR (since they're trying to HELP you, they didn't CAUSE the problem), apologize for the inconvenience, etc, you'd be surprised at what type of voucher compensation you can get. As a very frequent flier, the best advice I can give you is that crap happens when you travel, but the best way to get a happy resolution is to kiss major CSR butt. Otherwise, you won't see a dime.
