Bringing back retired workers to help out in a pinch is actually pretty common practice at Boeing. As Ken notes, they have existing procedures to cover it. I was having a beer with an old college mate a few weeks ago who's also retired from Boeing. They brought him back for a few months to help out with the requirements definitions for the planned MMA.
DeeVee, senior machinists/mechanics at Boeing are rather well paid - most make six figures.
The biggest problem Boeing is having right now is obtaining sufficient new LEAP engines - pretty hard to deliver a new MAX aircraft without engines. Word is that they have some loaner engines they use to fly new 737 MAX aircraft to Boeing Field then remove the engines and truck them back to Renton to fly the next aircraft to Boeing Field. They are simply out of room in Renton.