I don't think there's any way it could happen. Nobody put an asterisk next to the 1919 World Series or 1877 National League pennant, nor every batting championship won by a Colorado Rockie; the numbers are what they are, and the main goal of statistical record-keeping is to record what happened, however it happened. There are lots of events in baseball's history which are pretty iffy and will make your eyes roll.
That will not stop, however, a mental asterisk being put beside these numbers, and such an asterisk will be next to McGwire, Bonds and Sosa regardless of what Selig does. I'll sure have one.