Well the first rumor says it already. If by any chance Vitalik died then it will sent shock wave to Ethereum holders and for sure they're going to panic and immediately push the sell button. It's going to be a nightmare for Lubin (co-founder) to carry on the legacy of Vitalik and see that Ethereum can survived without Vitalik Buterin. Leaders really do matter in this market, and with enigmatic presence, Vitalik is very hard to emulate and if someone took his place it going to be difficult. Just like when Steve Jobs untimely demise.
Yes. That's what I've thought in the first place. Just like Apple with Steve Jobs' death, I believe that the same thing will happen with Ethereum. Apple has never been the same, after Steve Jobs' death (although it's still alive and apparently successful), and Ethereum could probably become the same thing as it lacks a true leader that would head the direction of development the right way.
But who knows? Perhaps, Ethereum would be able to live on its own just like Bitcoin without a leader. When this happens, then people would not be focused on a single person, but instead on all contributors of the network. This would make it much more decentralized than what it is right now, as the community guides Ethereum every step of the way.
Nonetheless, I hope that Vitalik stays alive and active on the Ethereum project for a long time, as his ideas would greatly shape the cryptocurrency for the greater good.
Just like I said, Ethereum will suffer, can go to 2 digits (worst case scenario). As Ethereum for me is also like Bitcoin now, a speculative assets that every news whether its positive or negative has a drastic effect on the price.
That could happen due to fear from investors within the cryptocurrency market. After Vitalik dies, the whole crypto community will panic, but it'll be temporary as prices start rising again. But yes, news either negative or positive will have a huge effect over a cryptocurrency's price within a short time period. It's something natural from crypto land, but what's most important is to have patience and keep hodling.