It is, but according to the salary sheet at baseball-reference he's made at least 52.8 million over his career before agents & taxes. He's married and has a couple of kids who will 8 and 12 next season. I could see spending a year at home with the family and trying to get over the physical pain. Cause right now the kids are at the age where they're fun, but in another couple of the years the oldest won't want him around. Teams are always after pitching, so he'll still get calls. If the pain goes away and he feels the competitive urge he could come back.
Radke did pretty good for the 4 or 5 innings he pitched.
I still don't know if I would invest in having him start, but he might be useful out of the bullpen to eat up some innings if one of the young kids has trouble with their start in the playoffs.