[rosnd]

I think the hardcoded IPs are typically only used as hints to initially resolve the root-servers.net domains.

[belorn]

Hints are used by the bind resolver software. It hard code the A -> M root servers and use those to initialize a cache. Naturally bind developers could change this behavior, and in the case that none of the hints works, the current behavior is to use a static compiled list that the software also include.

[rosnd]

Not just bind, unbound also. Unbound uses the hardcoded list of IPs to resolve a-m once and build it's cache, the hardcoded IPs are never used again.