Any one have an idea of what can happen if theses 1.1 Million BTC are sold at once ?
That cannot happen. There are many who are watching closely "satoshi addresses" and without satoshi coming into light, those may be considered stolen and getting frozen.
But the news for them being moved could cause quite a lot of panic, even without even being sold.
Is bitcoin in danger because a wallet hold that much ?
No. There's no relation between the amount in a wallet and Bitcoin security.
Keep in mind that Bitcoin security/viability is not the same as its price.
Do you think theses bitcoins are lost for ever ?
Yes.
What's your opinions guys about this amount of BTC in one Wallet ?
A wallet is a collection of addresses. There's no proof that "satoshi addresses" belong together, to the same wallet. Imho that's pure speculation.
However, you wanted an opinion, I'll come with one somewhat related: although the chance a collision (i.e. somebody else get the same private key for his address as an existing one) is incredibly small, it's not zero. So I would always advise splitting big amounts of funds between more addresses.