Back in the late 80s/early 90s, there was a small movement in a few gun rags to "de-sexify" the old designs, and the issue of "metal fatigue" was raised to scare greenhorns like myself from single action pistols. This issue had more to do with the hammer hook, but the long and the short of this is mostly bullshit, as is the case with most gun writing, because the awesomeness of 1911s and Glocks has been written to death and something new needs to be printed to keep readers interested, if not misinformed.
With respect to your question specifically, the mainspring, like all springs in a 1911 is a frequently disposable part that should be changed at regular intervals. The industry standard for the mainspring (as per Wilson Combat) is 5,000 rounds or 365 days for the purpose of routine maintenance. We all know that cars do not burst into flames with a 4,500 mile oil change and it is possible that the mainspring can function indefinitely (as could the recoil spring) depending on usage, but this is needless and negligent.
A 1911 is a fine machine. It asks a little more of the user compared to other designs, but it gives the user more in return. Simple maintenance of all parts at reasonable intervals ensures that these scenarios don't happen.