No, but if I were npm, I'd have an SLA guaranteeing three-and-a-half or four nines of uptime (which is far from unreasonable) and just accept that there might be times that signup is not accessible because that'd only cost me a couple hours of signups a year.

And no, I wouldn't have an alternative provider. It would not make sense to, if I'm paying a company to provide a service. Why should I pay another to do nothing?