Holding is very risky because you didn't know if the price of the coin you hold will return to it's ATH so, be smart and always take the risk. I think it's better if you hold the 50% and sell the another 50% to save even a little if your holding turn to lose.
And assuming it will return to its previous all-time-high and even more, base on 2017 and subsequent years, follows a long bearish trend. So it's really difficult, specially the question of when to sell. But I would agree that selling at 50% of your stash is good in the next bull run. And you have to consider the fact of the bearish cycle as well.
In any case though, nothing wrong with accumulation and the HODL. We all learn from the 2017 bull run so it's up to us on how to prepare for the imminent in 2021.