It's painful, but you can split your DNS across multiple providers. It's not usually done other than during migrations, but if you put two NS names from providerA and two from providerB, you'll get a mix of resolution (most high profile domains have 4 NS names; sometimes based on research/testing, sometimes based on cargo culting; I assume you want to fit in... but amazon.com has 8, and the DNS root and some high profile tlds have 13, so you do you :)). If either provider fails and stops responding, most resolvers will use the other provider. If one provider fails and returns bad data (including errors) or even can no longer be updated [1], the redundancy doesn't really help --- you probably went from a full outage that's easy to diagnose to a partial outage that's much harder to diagnose; and if both providers are equally reliable, you increased your chances of having an outage.

[1] But, it's DNS; the expectation is that some resolvers, hopefully very few of them, will cache data as if your TTL value was measured in days. IMHO, If you want to move all your traffic in a defined timeframe, DNS is not sufficient.