Fair question. But the reverse of that question is also true if we look at this logically rather than emotively.
Using an extreme to illustrate a point...if Cortese replaced Pardew with Morinho (spelling?) there wouldn't be one person on here saying: "what a crap move". Ok, we're highly unlikely to attract someone from those eschellons but on the manergerial scale if competence there is every chance a replacement for Pardew would be as successful as Pardew has been/could be.
So, yes, I agree, it would be a risk but that's what business decisions are all about - measured risk taking