Few things are as integral on a bike as a chain. You could ride a flat tire for a while if you had to, you could ride without shifting for a while if you had to, you couldn’t ride with a broken chain if you had to.
What causes chains to need replacing? It’s not stretching. Chains are metal pieces linked to other metal pieces using metal connections. They wear, they don’t stretch. Which makes checking them a bit of curious. A thorough and interesting bit on chains, how they wear and the various checking tools here. Every overly detailed investigation has its place though, and while many basic checking tools may be flawed, that doesn’t means your chain isn’t worn.
A few tips for optimizing chain performance and longevity.
1) use the manufacturer recommended chain for the your particular setup.
2) clean it with a rag and lubricate it regularly with quality stuff. Wipe excess lube before riding.
3) cross chaining (big ring in front, big ring in rear or small ring in front, small ring in rear) is murder on drivetrains, especially chains, as your asking the chain to work laterally. It hates that.
4) breaking it and reattaching it is not ideal, and really only to be used in a pinch. By the way if you use a SRAM powerlock, they are single use only.