I see several crucial mistakes, and I'm going to point them out because I really don't get why people keep doing this:

Mistakes made

• Depositing before downloading, saving and verifying the Letter of Guarantee
• Sending a large amount of Bitcoin to a relatively small and unknown service
• Sending your entire Bitcoin savings at once to a third party
• Keeping your life savings entirely in Bitcoin

All of this means you literally have no proof whatsoever to backup your claims, while you could and should have had a signed message. But even then, a one-man operation could be very tempted to take such a large and for many people life-changing amount of Bitcoin. Selective scamming has happened before and will happen again. It's trival to add a "if amount large enough, then don't return it"-setting to the server routines.

I'm following this case to see how it evolves. In a similar (but much smaller) case the mixer said the funds were sent to a different address: