NS record, nameserver down.

[fddi]

Hello,
I have a domain.com

with w nameservers defined, for example

;; ANSWER SECTION:
domain.com.        86400    IN    NS    ns1.domain.com.
domain.com.        86400    IN    NS    ns2.domain.com.

;; ANSWER SECTION:
ns1.domain.com.    86400    IN    A    172.16.16.1
ns2.domain.com.    86400    IN    A    172.16.16.2

;; ANSWER SECTION:
www.domain.com.    86400    IN    A    172.16.16.80


ns1 and ns2 are two nameservers with DLZ backend on mysql so the 
architecture is multi-master.

I wanted to ask what happens if one of the nameservers is down and a 
remote host wants to resolve
a hostname on my domain.

let's say ns1.domain.com. is down

if a remote host does a query for www.domain.com will the query always 
be succesful even if ns1 is down ?
or the NS records are just round-robin so that if the query arrives to 
the one which is down, the query will fail ?

thank you

Rick