It is a fact many altcoins survived the crypto winter back then, some examples are ethereum and litecoin, but there were many other altcoins which survived too.
2) Why do Bitcoin survive during crypto winter and other crypto's finds it difficult to cope ?.
Why do you think bitcoin would have died back then? Bitcoin suffered a huge setback, that is undeniable, but at the same time while the crash was terrible, it was not as if the technology behind bitcoin had suffered any kind of attack or an unknown vulnerability was reveled at the time, bitcoin was still as solid as a technology as ever, and as such it had no reason to at all to disappear.