An opened bottle of Irish cream liquor can last for several months when stored properly in the fridge. The key to extending its shelf life is to ensure that it is tightly sealed and kept in the refrigerator at all times when not in use.
Since you mentioned that you took a few sips from the bottle, the exposure to air may have caused a slight reduction in its shelf life compared to an unopened bottle. However, as long as the bottle is tightly sealed and stored in the fridge, you can generally expect it to remain good for around 6 to 12 months.
It's essential to look for any signs of spoilage before consuming the Irish cream after an extended period. If you notice any changes in smell, taste, texture, or appearance (such as curdling), it's best to discard it. Additionally, check the bottle for any expiration date provided by the manufacturer, as it can give you an idea of the product's intended shelf life.
Remember that liqueurs like Irish cream contain both alcohol and dairy components, so they can spoil over time, especially if not properly stored. If you have any doubts about its quality or safety, it's better to err on the side of caution and replace it with a fresh bottle.