This situation has been coming for a very long time (getting rid of 401k match), and it won't be the last action taken before it all goes to pot. Setting aside the discussion as to why they are doing this (cash flow deficiency), the RBA returns will be at best on the order of US treasury bonds or stable value...any young employees who are stuck on this plan won't see any great returns from stock investment. That's assuming that IBM management doesn't mismanage the fund into oblivion first (paying out bond-level returns to the employees while placing lousy speculative trading bets with the money).
Young employees can, should and IMHO will leave...there are too many reasons not to stay. Other tech companies offer much better working conditions and employee compensation, not to mention more and better opportunities for career advancement. The writing has been on the wall for a long time, but now that writing has turned into bright, shining, spray-painted graffiti.