Nitrogen is a preservative, so Nitro cold beer lasts longer than regular cold beers. However, the expiration date shown on the can may not be much different from that of regular cold beers. For example, my Starbucks Nitro Cold Brew can was dated 5 months after purchase. Since nitro coffee is made with cold coffee and stored at a low temperature, oxidation will occur much more slowly.
Even in a fridge, it will decay at that temperature. The taste will change over time. Yes, any bottled beverage will go bad after its expiration date. Compare its shelf life with that of, for example, cold coffee or nitrogen infusion, the latter can stay in the refrigerator for a long time.
However, if you choose to let your beer sit cold in the refrigerator, let it sit for longer than it would at room temperature. In addition, cold coffee is naturally lower in acid, helping those who are prone to acid reflux or have a sensitive stomach. This means no more than two or three weeks in the barrel for optimal results with homebrewing systems such as UKeg Nitro or Royal Brew and several months for a commercial nitro coffee barrel. If you add something to your cold beer concentrate, such as sweeteners or even plain water, the shelf life of cold beer decreases.
As for the perceived sweetness of cold-brewed coffee, the base of all nitro coffees is inherently less bitter and has less acid than regular brewed coffee, making sweeteners unnecessary. If you've ever tried to save a few dollars and use a household carbonation system to add CO2 to cold coffee, it probably didn't take long for you to realize your mistake. Once you have the cold beer concentrate or diluted beverage ready to drink, you should store it in a properly sealed container. This is because cold coffee comes with different components and can last much longer in the fridge.
However, if you want to get hold of a cold coffee maker, you can take a look at the Toddy Cold Brew system designed precisely for cold brewing coffee.