I don't understand that you assume Bitcoin is mandatory. Bitcoin is surely the main coin, it is like the mother of all crypto coins. However, it doesn't mean altcoins can survive without Bitcoin. Altcoins have their own ecosystem, altcoins have their own market. I think altcoins can survive although Bitcoin disappears. As long as we have exchanges and crypto market, altcoins will be there to trade by any people around the world.
omg... your opinion is against the current, and I like this kind of discussion... sometimes unexpected things do happen, so I also appreciate this opinion because it could happen...
simply, to see if altcoins react the same as Bitcoin depends on which aspect is attacked... if the attack is on cryptocurrency as a whole, then when Bitcoin goes down, altcoins will also go down... both are in the same space
whereas if only Bitcoin is attacked, it is likely that only Bitcoin will experience a price drop, because altcoins are not included in the Btc world...