I made an hypothetic TA on a possible apocalyptic crash of BTC/LTC/ETH, check it out ! (it will recover after that if it happens, I'm sure of that).
https://steemit.com/bitcoin/@adri1202/btc-ltc-and-eth-apocalyptic-hypothesis-i-ll-hodl-no-matter-what-and-btfd-if-some-conditions-are-met
I also think alts goes up because BTC goes down, BUT, when BTC will explode again (and it will in some weeks), alts will crash for some time, then investors will diversifie their investment in alts, maybe just to grow their BTC capital by trading on BTC pairs while BTC continues to go up.
What has also to be taken account of is the fact that some alts have a tech that BTC has not and will never have, of course all alts that are only some random currencies wannabee will crash (besides LTC/ETH/BCH imo) but when a tech, an app, or some specific currencie use (like THC, you can laugh but it can be usefull and away of BTC volatility) will stay and grow.
Like in the 'internet bubble', a lot will try, few will succeed, but overall the crypto world will go up and up. The real game changer will be smart contract on BTC, ETH will be in trouble, and some independent alts, even with an good and original tech, will take a hit because the BTC smart contract token will have a better reputation and will seem safer (true or not, it's what investor will think that counts).