I've never heard of the site you linked, and from the display containing dates as old as 2005/2008, it looks like this site is fairly old. It's possible that it's being kept up-to-date, but maybe not.

Have a look also at https://en.wikichip.org/wiki/mirc/introduction
and there's a #mirc or #mircscripting channel at most of the larger networks, some more active than others

Your example is not faithfully following the examples at the page you linked. While there are often several valid ways to do the same thing, you avoided them all, lol.

You should not follow the end-curly-brace with anything except a command separator.
"IF" is a command not an identifier. While it's common for identifiers to have the parenthesis touching themselves, you cannot do that with any command or alias name, so by having the parenthesis touching the 'if' this confuses the scripting engine. Try like:

Code
alias F2 {
  var %n = $input(What's your nickname and password?,e)

  if (%n == $null) { 
     echo "nick change canceled." 
    }
 else {
      tokenize 32 %n
      nick $1
      quote nickserv identify $2
  }
}

Another way you can do things is to take advantage of the behavior that anytime you have an identifier that uses $$ instead of $, if the return value is blank, it halts the script. so if this used $$Input instead of $input, you wouldn't need to handle the case where it returned $null