Got a quick question for you: our church board here is divided in its opinion in "how long cables should last." ... Some of our cables (standard garden variety XLR & instrument cable... LiveWire grade, not expensive/premium cables) have died. We haven't replaced cables in 1 year. Our church sets up & tears down twice a week, 52 weeks a year. I tell the church board that we need cables, and cables going bad is no surprise.Thanks for the question, Andy.
In short, a microphone cable should last you at least 10 years.
Now for the more precise and extended answer...
First, Andy is absolutely correct that "cables going bad is no surprise." Most cables set up and torn down twice per week will stop functioning properly at least once every couple years. However, most cables can be repaired easily with a soldering gun, solder, wire cutters, and a cable tester. There are tutorial's online that explain the process. Here's an example of various wiring schemes that I pulled up from the top of the list on a Google search for "microphone cable repair."
Typically, cables stop working because the wire and the connector are no longer attached to each other. Those "broken" cables can be repaired. Sometimes, however, the cable itself gets damaged by being crushed, bent strangely, or wrapped incorrectly. This will typically lead to significant loss of voltage, shorts within the cable itself, or noise when the cable gets near an electrical source or cell phone. Throw those cables away (after cutting off the connectors for spare parts). But be careful. These symptoms could also occur as the result of a repairable problem, so troubleshoot first.
At Covenant Life, we have quarterly repair days, called Work Days, when we test and troubleshoot all our broken cables. Sometimes we throw them out, but we repair all that we possible can. We've found that four times a year is a good rhythm to ensure that we have enough cables to keep each of our systems functioning. However, that only works because we have a plentiful supply of extra cables in various types and lengths. If you don't have extra cables, you may need to repair them ongoingly.
One way to ensure that cables last as long as possible is to wrap them up using the over-under method. This is the first thing I train our new tech volunteers to do, and I highly recommend this video to see how to do it yourself. Cables that have been wrapped around the arm or with the over-over method will deteriorate much more quickly and require replacement rather than repair.
Finally, an honest note from the leader of a great volunteer team: setup and operation of a sound system can be stressful for non-experts, especially when things aren't working correctly. While I'm not saying this is necessarily true at Andy's church, my experience is that roughly 3 out of 4 cables labelled "BAD" by a volunteer are actually working just fine. There was an operator error somewhere in the process, and in the hurry to get ready for the service, the cable was incorrectly placed into the repair pile. Anyway, just another reason to test before tossing.
While they do require some care and feeding, your mic cables should last you quite a long time.