Would be completely useless as a Hamilton replacement. Di Resta is a copy of Button. He's got nothing extra, doesn't do any exciting overtaking in a race. The last thing McLaren needs is two of those drivers. Pérez would be a far better choice if McLaren needs to replace Lewis.
Perhaps having two drivers of similar driving styles is a good thing, then the new car wouldn't have to be catering to two styles. Just a thought...
A good solid drive from PdR today, not that the haters will see that.