Eight years is a bit much, isn't it? Is he really that unquestionably proven to where you would commit yourself to him for that long of a time? I haven't really followed Newcastle enough to say how good of a manager Pardew is, but I would only support that long of an extension for practical legends a la Ferguson. I know Newcastle has been plagued by instability, but at the same time the solution shouldn't be tying yourself to one manager for so long either.
I'm sure they aren't on the hook for eight years. If Pardew chews out some bad results I'm sure they have a mechanism with which they could use to get rid of him.