> the technology in which they are an expert is obsolete

A lot of the principles, idioms, patterns, and instincts experts pick up transcend technology. Sure, they won't be able to optimize a framework they've never interacted with, and some bugs will probably require a trip to stack overflow, but they know how different pieces fit together, where to go for help, what it looks like when something isn't working, best practices for avoiding a huge catastrophe, and - probably most importantly - the wetware people skills required to get things done and done right.

Being a master software engineer, in other words, has almost nothing to do with the particulars of the software.