Can you still make lumber from a dead pine that's been standing for 5 years? Over here it would be molded, insect eaten and half rotten.
Depends on the species of pine, damage done to the top, where the beetles attacked it, how quickly the bark slips, wet weather, lots of factors. But typically, if it stays dry, the wood will stay usable for a long time. Probably not the best storage option for wood, though. Most of the ones I think I can use are probably only about 2 years dead, but are still a result of the beetle infestation. One quick look at the top of the tree will tell you if it's still got usable material in it. If the top is still relatively intact, still has small limbs and even pine cones still in it, it very likely has good material in it. If large limbs are breaking off because they're rotted, probably not. The trick is to fell it without destroying it. The longer it stands there and the dryer it gets, the more likely it's going to shatter when it hits the ground. Dried wood isn't nearly as resilient when it hits the ground. A dry pine will typically break in several places when it hits, which is also what makes them so dangerous if they do get rotten while still standing. We call 'em deadfalls or widow makers down here. They're extremely dangerous to cut down once they're rotten. There's almost no way to control the direction of the fall, and sometimes, just the inertia of it starting to fall over will make the top break out and fall on the sawyer. Don't even think about trying to push one over with a tractor unless it ain't much taller than the tractor. The good part about air-dried wood is that it doesn't warp after milling. Most trees grow in a spiral chasing the sun through the seasons, so it's hard to cut lumber that won't twist without kiln drying it.
Another thing that will get beetles started is when something else kills a tree, such as a lightning strike. It's like a pine beetle buffet, then, with the good stuff just a few bug steps away. I had a massive pine about 100 feet from the house that was nearly 30 inches in diameter at the base that was killed by a single strike a several years ago. There was probably at least 1500 board feet of lumber in that thing. I was looking straight at it when it happened. That one strike took out the pine as well as a pretty good sized water oak that was about 20 feet away from the pine. The strike stripped every shred of bark off the water oak from the ground up to about 30 feet high, and there were huge craters around both trees from where the roots exploded. I didn't really realize the pine was also hit until I walked out there to look, because there was that glistening naked water oak standing there. Was petty obvious that tree was not gonna make it. We were watching TV that afternoon with a storm blowing in, and my then 6 year old granddaughter was laying in the recliner with me, nearly asleep, but claiming to be afraid of the storm. Truth is, from the time she could walk, if I was in the recliner, so was she until she just got too big for either of us to get comfortable. I was watching the trees sway back and forth, and then BOOM! A huge orange plasma cloud, bark flying everywhere. I found pieces of my trees in 4 different neighbors' yards the next day. The 6 year old's reflexes were kind of amusing when she launched. She must have levitated at least 18 inches straight up. It wasn't nearly as funny when she came back down on top of me. She's always been strong as a mule and tough as a pine knot, all muscle and bones. She is not a fluffy little couch potato. She's worn out 4 or 5 bicycles in her short 12 years on this planet, and NEVER stops moving. She's like the Looney Toons Tasmanian Devil. Refreshing to see a kid that will actually get outdoors these days.