I put D'Addario Chromes on almost all of the basses I build and sell. Most of my customers still have the original set on there, even going back 15 years. I still own a few of my earliest basses from 1997, which have the original Chromes and LaBellas on them, and they are fine.
To me, there are only a couple of ways that you can kill a set of flatwounds:
1.) You can wear them out. If you play long, hard hours, you'll shorten their life. Usually, the outer wrap will snap on the A string. But still, they last a long time. The Chromes on my main gigging bass, which I play maybe 3 hours per week, have been going strong for six years so far.
2.) They can rust out, even the stainless ones. If they sit unplayed in a humid environment for some years, they can start corroding and get really dead sounding. If you have a flatwounds bass that you keep tucked away and don't play often, it's a good idea to keep the flats "greased" a bit. Any of the commercial string lubricants will work, or you can use Mineral Oil, available at the drug store. Mineral Oil won't hurt the bass or the fingerboard, and it's a lot like natural finger grease, but without the acids.
3.) You can damage them by nicking the outer winding on something metal, or by swapping them back and forth on the bass. That will shorten their life.
Other than those things, good flats will last for decades. I've had vintage Ampegs come in my shop with 40+ year old LaBellas that were still reasonably playable.