In my opinion altcoin market can't crash easily because there is a huge amout of money in altcoin market. However don't forget, everytime alternatives are good choose choices. If there is no alternative for Bitcoin for example, market will be affected a lot from it.
It already did, check coinmarketcap website and see the actual price list now. Most of the coins declined 30-40% down now. The most stable ones, BTC and ETH also decreased a lot.
I'm not even talking about useless ripple trash. It's clearly down.