First time pumpkin grower here as well, but my leaf problems consist of terrible powdery mildew. Hope someone more knowledgable than me can help you!

I don't have a specific diagnosis but if this condition is on the early/oldest leaves and the newest younger leaves aren't affected then it may just be from wear & tear from a brutal summer?

If your variety is nearing its maturity date, and especially if these are older leaves, it could be part of the natural process, die back and getting ready for harvest. I try to time my planting so they'll mature in Oct (put 110-day seeds in ground in early Jun). I had miniature variety volunteers pop up in Apr. I let them do their own thing - they matured and the vines already died back last month. Which is just as well since powdery mildew is starting for me now.

Yes, hard squashes will continue to ripen off the vine in a sunny spot (outside if weather is still good, or inside by sunniest window). It may take weeks depending on how far along it was before it was plucked. If the skin starts to get soft, use right away. If it continues to color and harden, keep going until its all the way cured (hard skin).

VG - try a 50/50 milk and water spay on your powdery mildew. I've had some success with that if you catch it early. Also, I usually cut off the mildewed leaves - although I have no idea if that helps or not.

You don't write where you are. The diagnosis may vary depending if you are in zone 8 or zone 4 for example. It could be also good if you showed us the whole plant, not just one or two leaves. Having said that I am leaning to think it is not any kind of disease, but a condition caused by the weather and/or by the end of the growing season, as other posters already said. If fruit is still immature I would leave it to ripen on the vine. And no need of destroying the plant!