IMO it is depend on how the development of your coin are? If it look like can't develop & stuck it is better to sell your coin before it is become zero value.
but if you look at crypto conditions now that it becomes irrelevant, you can see that almost all crypto are not currently developing in the market, does that mean we have to sell them? I don't think so. it all depends also on the conditions of the team, where they work and still run the road map or are silent. we can see it from the updates made by the team every week or month, I think it is important to consider.