Depends. Electronics manufactures won't promise any CPU will be available for that long (Odds are someone reading this should be thinking I'm partially responsible for that policy in my company). When spare parts are not going to be made the companies will try to predict how many will be needed in the future and order that many. This will be your biggest limit: you need a part there is a good chance the part is failing more often than expected and so the manufacture is out of stock and they cannot get more. (or sometimes they can, at a cost of $1000 each, minimum order 10,000 - the manufactures want to sell the new shiny replacement even though it isn't compatible)

Even if the above isn't an issue, storing electronics not on a circuit board is not easy, but I'm probably not supposed to talk about those issues. (You can research them)