But can Some coins just disapere? Or Go to Zero?
Yes, the really bad ones will do one or the other eventually, as people lose interest in them and figure out that there's nobody mining them and isn't a market for them. It's already happened to a lot of coins that yobit gives away for free.
I Think If market is Red its a Good time to buy!
That's a good idea but only if you pick the right coins. Any of them worth 15 sat or less (and that's only my estimation) are doomed. It's funny because dogecoin has always had a low valuation in terms of satoshis but it still retains a very strong, supportive community. But dogecoin is an exception to the rule. Very cheap coins are usually priced that way for a dam good reason, meaning that they hold little value. Either stick to bitcoin or to the top coins on coinmarketcap.
when altcoin prices fall and flush like that it should be a very good point to buy altcoin as much as you can and take advantage of lots of panicked traders to buy altcoin at cheap prices.
Obviously that's what you should do if you see some value on the altcoins that are dropping.
And it's hard to see that value sometimes, because there are so many coins in existence and nobody knows which ones are even going to survive. It's a great idea to buy low and sell high, but you have to pick the right coins. That's the really hard part for any trader/investor.