I can see why you think the plant may enter senescence after the seeds are done - it's a reasonable guess - but it just doesn't work that way.I thought that when the seeds are done & mature, the plant will soon be starting her "death process" (senecsence?)
In fact, in this particular rather extreme sativa the seeds were done before it even started developing trichomes!
And don't forget that true equatorial sativas are putting out new pistils all the time.
So even when the plant is ready to harvest, half of it is covered in brand new fresh white pistils, which need to mature... you could keep harvesting for a looong time. This only really apllies to equatorial sativas, of course.