Dump it where? Who and what can buy that many at a time? What exchange? How would someone cash out 1 million ETH into fiat? None of these scenarios of dumping make any practical sense and are just FUD.
First show how it is possible to dump enough to crash the bubble. Panic sells from day traders and career speculators isn't going to crash the price if it is a bubble unless you believe the vast majority involved in the space are day traders and speculators. I don't think the vast majority of holders will be day traders and speculators.
If millions of people hold ETH for 4-5 years, then the price I would think will be pretty stable. People who buy Bitcoin often buy it and put it in cold storage for years. Some will buy ETH and treat it like a long term lottery ticket and not touch it for 5 years or until they retire. So with that mentality, it will not matter what the price is that day, or that month, as long term holders don't care if it's a bubble or recession as long as the space as a whole is growing.
Even a failed ETH isn't going to go away. It will stick around for 5-10 years with a high market cap in my opinion. It's just if it fails another tech will eventually acquire a higher market cap.
I fairly agree with you Dana, Ethereum is not going anywhere for the next 2 or possibly 5 years as investors are still seeing this as a great tech which can grow significantly. Hence the dumping of large ether as suggested in this video by @majorleaguemarc will provide a great opportunity to buy the dip for long term investors. As I mentioned earlier, I see Ethereum as an IOS / Android app store for block chain startups so it's definitely here to stay!