If a person has lost 80%, this means that the trader is so-so. He was thirsty for profit. I think they should have understood that this will happen. Especially buying Bitcoin at the peak of its popularity was a dubious investment for them.
80 percent is a lot , I also think if the trader has lost so much then he needs to revise the strategy , I think if such a percentage is in the red I think you just need to keep the token and not sell