Before your friend decided to invest in crypto he supposed to be know what kind investment crypto is. When the price down like a crazy it pretty normal in crypto because crypto is so volatile, my advice for me just DCA and set your own goal so you will know when you already reach your goal then you can Quit.
I would advise to not set a DCA and don’t to set a goal. Whenever there is necessary or requirement of funds, then only one should cash out the Bitcoins. These Bitcoins are very rare, so if you set a target and sell it, then definitely you won’t get the full profits or potential of the coin. Bitcoin’s price always goes up, so yes Bitcoin investment should be for long term always. Take the advantage when the price is low and keep on accumulating and storing Bitcoins at regular intervals.