From the close-ups I cannot see any of the characteristic blight spotting on foliage or stems. From the amount of defoliation, if this were blight I would also expect to see dark purple/brown patches on many of the stems, but I can`t.
What I see is lower defoliation and pale green (but apparently clean) tops, rather than the normal deep green colouration. This is not normally symptomatic of blight, but it does indicate that the plants are dying back, and I suspect wet weather rather than any more sinister cause.
I certainly think that the plants are now too far gone to make any further crop growth, and although I do not think blight is present I would cut them down and remove the haulm as a precauthion.
Don`t lift them for at least 2 - 3 weeks after removing the haulm.