That is stating the obvious! so surely we need to see who the new manager is and then how he performs before deciding if it was a mistake or not!
We do not have all the facts we do not know the plans going forward and do not understand NC's reasoning at present so all opinions to date on this site are based on speculation and nothing else.
All judgements on whether the sacking was or wasn't a mistake can realistically only be done from the future looking back and even then there is an element of speculation involved as we will never really know how Pardew would have performed by comparison!