You'll know when your lift stops engaging because of the bolts breaking. That's not to say broken lift bolts is the only way that lift can stop engaging, it's just one of them.
And yes, preventative FTW.
Tip: get a clean connection with the socket you use and unbolt cleanly. Those bolts (as with many on the car) are made of cheese and if you round them off, you'll have a hell of a time trying to get them off afterwards. Ask me how I know.