But bitcoin alone is not an income. That is if you're not doing anything with it, anyway. So talking about alternative income doesn't really make any sense here since technically he had no income at all.
That will be a lesson for OP's cousin and he should change his life plans if he doesn't want to be in this situation again. But I don't think investment will help us in case we are unemployed because there is no guarantee that investment will always bring profit. Investment needs to have a long-term vision and must be completely separate from daily needs, only taking profits when the set goals are achieved. I think saving will be more effective in case we are unemployed than investing.
Investment is only good if you've already done it, and it's only going to help you not run out of money. It won't help you if you're trying to make more money.