You can hold for ever if you stop being so fiat centric. Don't get me wrong, in terms of trading, there are indeed targets where you buy and sell, but when it comes to the coins that you hold, there is no point into selling any of them in the forthcoming years. I personally won't end up selling of my cold storage coins at all. It feels amazing that I have wealth stored outside the banking system, and that alone is worth way more than any short term profits I could gain by selling them. The main point is that you are exempt from any negative side effects that this on debt based system exposes everyone to. That alone should be reason enough to make people hold a certain percentage of their coins without any intention of selling them later on.
At some point you'll be able to buy your daily needs with Bitcoin, pay your bills, pay for gas, etc, where fiat will then be nothing more than a redundant loser currency. It may even come to a point where people don't even want to sell you their coins for fiat anymore, think about that. It's far away at this point, but not impossible, and I believe that there is a significant chance of this becoming reality in the future. If you believe in that, you will not sell any of your coins for actual fiat right now. But hey, do what you want, it's your choice after all.