It depends on the well and choice of the holder what he can do to his Bitcoin but asked for suggestions I am going to give my two opinions and both are the best just pick one and use it. The first one is as you mentioned in your post to not sell your all bitcoin in one bull run there must be another one that comes after this and when you keep your bitcoin then you do not need to buy bitcoin for the next bull run and its price will increase definitely from the last one. The second one is to sell your bitcoin in a bull run and the reason behind it is when you sell your bitcoin in ATH it will give you a high profit and you can easily do something on that profit we know the price of bitcoin is volatile it goes up and down and let say if you need money and market is down then you will definitely selling it on loss. But when you sell it in ATH and grab the money for the next bull, you will buy it in the bearish market and sell it on the bullish market it will give you more profit than keeping it safe for the next bull run.
We're quite a long way before we can start discussing whether we'll sell all our coins or not. I believe that the majority of long-term holders aren't planning to sell before seeing a new ATH, which is reasonable. If Bitcoin is capable of surpassing $70,000, then it's capable of climbing even further; the most recent ATH isn't the limit. Moreover, at this point, it's unlikely you'll sell because the momentum during the bull market is susceptible to raising the price even further.
Personally, I don't know how I'd react. Supposing Bitcoin reaches a new ATH, that would mean an average of 3x yield, which is pretty extravagant if you carefully consider it. Some prefer to sell 50-50, splitting the sale into two or more different times; it only depends on personal preference. If I were to sell in two years, during the bull market, I'd prefer to keep some Bitcoin in hand rather than sell everything at once.