Do you think altcoins can survive without bitcoin leading the way ?
This scenario will be catastrophic if it ever happen, no i dont think that they will survive, bitcoin has been leading the coins for years now and if bitcoin fails investor will likely think that other coins may end up the same fate.
will the bitcoiners that lose faith go into altcoins or will they
just cash out and take profits ?
Maybe they will just get what ever money they could get and move on leaving crypto currency.
Bitcoin has no exemption for loosing it's value when major catastrophic event will happen that causes shutting down the whole internet so this is one kind of world event that will cause massive effects for Cryptocurrencies because Bitcoin and digital Currencies are Internetwork dependent and will lost its purpose and value.