The simple model to use for comparison is IE. Microsoft let the product languish once they snuffed out Netscape and seemingly let it rot until a viable competitor in the form of Firefox emerged. Since 2004, IE has lost between 20-30% market share depending on the source that you use.
Despite this, IE still holds a market share in the 65-75% range, and there is still no talk about either de-integrating IE or making it open source. I honestly think that if MS ever takes one of their core products and decides to go full open-source on it, they're essentially giving up on it. It just seems like the mentality they'd take.
"A child is a person who can't understand why someone would give away a perfectly good kitten." -- Doug Larson