IMO, the blame lies solely with the CEO, because he is still to retract his statement regarding snapshots not being backups (despite their site selling them as backups to the end-user), and for not accepting the fact that for someone controlling business data that creating backups AND regularly testing them via restores is 100% essential. Culture trickles down, and if the CEO only accepts blame and not the reason for the blame then it's a sign that they won't learn from the problem - and that's the biggest red flag you will ever see in ANY business.
I can only see one way back for them that won't taint their reputation completely. They need to:
* Post a full post-mortem of what happened, how it happened, how they fixed it, and what they're going to do to ensure it never happens again.
* Issue a full apology for the problem. Accept full blame, and accept (including the CEO on Twitter) that Gandi failed to follow accepted industry standards.
* Sit down with the engineers that work at Gandi and hear their grievances. While I doubt that their engineers knew this would happen, I'd be willing to bet that there is at least one person there that had raised the lack of off-site backups and no recovery mechanism. That person needs a promotion, and whatever resources needed to fix Gandi.
* Issue a full refund to those that lost data - not a small discount, as already reported. A discount is a kick in the teeth, whereas a full refund is the start of a real apology for failing the customer. If you go for a meal at a restaurant and find broken glass in your food, the first thing the server will do is give you a full refund, no questions asked, regardless of how expensive your parties order was. Gandi need to take the hit, and live to fight another day.