I heard the split happened when IBM licensed the process it developed with huge amounts of GloFo investment to UMC sometime back. That's when GloFo moved a large number of its employees out of Fishkill and started developing processes on its own. This hurt both GloFo and IBM - GloFo struggled to get 20nm to yield on its own, leading to licensing a process from Samsung at 14nm. IBM's semiconductor division lost a valuable partner who was putting in money and resources - this coming at a time when they lost the game console business was a death knell.
Its amazing how that one decision from IBM management to license to GloFo's competitor cost them.
Remember, you cannot shut down the fabs and lay people off... those would be the terms of the agreement. That's $1.5B of losses per year, which, even with $1B given by IBM, would lead to $0.5B of loss in the first year. The second year would be, again, around $1B of losses... I wish I had $1.5B to burn for the next 2 years :-)