Teams don't always provide a lot of information about player injuries - I'm not sure anyone outside the organization knows the timetable for Morneau's return (who knows - he might already feel back to normal). His return of symptoms came towards the end of the 2011 baseball season, and the Twins were out of contention by that point, so he simply went on the disabled list for the remainder of the season. He has the next few months to rest up and gradually get in shape for next spring, assuming he decides to keep playing.

According to wikipedia, the hockey player Patrice Bergeron had a serious concussion in 2008-09 (out for about a year) and has since had a productive career, despite having had a couple of more concussions that caused him to be out for much shorter periods.

I think the bottom line is that you can't predict these things, and everyone is different. I would think it would be important to take good care of yourself and "do all the do's" required to support your recovery the second time around (which includes being patient). Hopefully it won't take as long this time - best of luck.