Difficult decision, in my opinion. It has been quite some time since he last performed at an acceptable level for Newcastle. He is 33 years old. Experience is good, but he is declining. Mentally he has looked "gone" for a very long time.
On the other hand, we are actually talking about selling Coloccini BEFORE getting rid of Williamson and Taylor. Also we do not have any decent CBs lined up for replacement. It's a bizarre situation.