It's down to the mount options, use 'soft' and the program trying to access the (inaccessible) server gets an error return after a while, or 'intr' if you want to be able to kill the hung process.

The caveat is a lot of software is written to assume things like fread(), fopen() etc will either quickly fail or work. However, if the file is over a network obviously things can go wrong so the common default behaviour is to wait for the server to come back online. Same issue applies to any other network filesystem, different OS's (and even the same OS with different configs) handle the situation differently.