That's the big takeaway here, in my opinion. Regardless of the fault with MailChimp (and I do think they're at fault here), you should never rely on a free serv

That's the big takeaway here, in my opinion. Regardless of the fault with MailChimp (and I do think they're at fault here), you should never rely on a free service if it's mission critical to your business and there should never be a single point of failure like this. If this really was as critical as OP claims it is, then they should have taken more care to ensure that this wasn't even possible.