I think it depends on the altcoins that you are holding. If the altcoin your holding is not good you can sell it all and buy bitcoin. But if your altcoin have so much potential yo be good keep holding them.
Also depends on whether he bought it at a low price or a higher price. If he bought in early at a low price then it would probably be wise to hold and only sell a little bit, assuming that the market will go back up