Pardew is now the bookies favourite at 4/11. Those odds would suggest it's more or less a certainty, especially when you compare that to the nearest one's they're offering:
Other odds are:
Rowett 4/1
Hodgson 6/1
Irvine 14/1
Warburton 16/1
Maybe they were fearful he'd get a positive result against Blackburn tomorrow? Getting rid now gives them time to get someone in before the international break starts. That way it gives the new person time to get to know the squad before having a fixture and will allow them to soon start...