Generally speaking, when you spend $200 on an electronic device these days, it either works or it doesn't. And when it finally does break down, it's pretty much disposable.
I dunno about you but the notion of keeping a $200 keyboard in perfect working condition for 20 years is pretty much impossible unless you store it in a glass case and play it only on Ash Wednesdays.
Stop worrying about whether or not the keyboard will last forever and simply learn to enjoy it while it lasts.
Parts may be readily available now, but 10 or 15 years down the road it's anyone's guess. People will repair a $3000 Kurzweil until doomsday, but $200 to $700 Casios probably not. Simply because there's no money in parts and service for what is essentially a disposable product.
Like I said, focus on learning to play and enjoy your keyboard while it lasts but like any other tool of the trade it will eventually wear out. When and how that will happen depends on how hard and often you play and how well you take care of it while you own it. By the time it finally dies on you there will doubtless be something ten times better available for the same or less money so it will eventually become a non issue.