Actually you don't need the if and elseif statements if you use the /goto:

on @*:text:$($strip(!chance)):#: {
  if (!%f) { set -z %f 5 | var %chance = $r(1,9), %msg = msg # Congrats, you won $&
      | msg # So you want to take a chance on something? Let's do it. | goto %chance
    :1 | %msg a voice | mode # +v $nick | halt
    :2 | %msg a kick | kick # $nick Better luck next time. | halt
    :3 | %msg a halfop | mode # +h $nick | halt
    :4 | %msg a ban | mode # +b $wildsite | halt
    :5 | %msg a ball | .describe # gives $nick a red ball. | halt
    :6 | %msg a rabid dog! | .describe # gives $nick a rabid dog that mauls them to death. | kick $chan $nick You died. | halt
    :7 | %msg an Xbox 360! | .describe # gives $nick an Xbox360 with Call of Duty: Modern Warfare 2! | halt
    :8 | %msg a memo! | ms send $nick Congradulations. | halt
    :9 | %msg a website! | .msg # $nick http://wolverines.ning.com/ | halt
  } 
}

A trigger control is added so users can only use the !chance command every 5 secs to prevent spam.
P.S. I don't see the need for timers.