The proof about why wooden sash windows will last longer than modern plastic sash windows is in the older homes. There are houses that are one hundred and fifty years old and older than still have the original wooden sash windows.
If these houses exist in climates where it rains a lot or snows unmercifully, chances are the windows have been beaten up and needed to be restored over the years. But this is possible with wooden windows, and not with the plastic ones. Further, if the wooden sash windows are well maintained, they may last another several decades or more.
The way homes were built a hundred and fifty years ago proves that the structure was sound, and the windows are still more or less intact. They did not have sealants, but somehow these windows stood up to the snow and rains.
Plastic windows are durable and strong. They are pretty, and modern looking. The are clean and can be purchased in any color you like. And you will probably never paint them. That is because when the elements do get to them, and they start getting brittle and chipping and peeling, it will be time consuming and not very cost effective to try to refurbish them. You would need to sand them and paint them, and to do that to plastic, well, the results will be less than perfect. You will probably be better off just purchasing new ones in the long run.
While redecorating, it will be a pleasure to purchase new plastic windows. Even though they are expensive, it is worth it to have your home look stunning and modern again. And with little maintenance, just regular cleaning really, they will stay looking beautiful for up to ten years or maybe longer. This is what type of guaranty to may be able to get for your new plastic windows. Maybe some companies will guaranty them for 20 years, but not much more than that.
There are companies that restore hundred year old windows and older. They can make these windows look like they did when they were new. The restoration process may be costly, and some windows may even need to be replaced completely, but they will now be treated and sealed and will last perhaps another hundred years, with regular maintenance.
So, while thinking about purchasing new windows for your home, just do a little research and find out why wooden sash windows will last longer the modern plastic sash windows.