I dont think you can encourage anyone to stay when they already lost money.
Just tell them that crypto is not a game. You have to do your own research. If you lose money it is your fault.
People come and go, they have rights to do what they like and your comments will not matter at all. It's about how to respect the decision of others based on what they feel/felt. This thing can change if you have a word of wisdom and putting the positive thoughts on the mind of one person. But when the loss come first, it will be hard to... and nothing you can do.