Sorry, but I don't get your point. you can debug with echos that easy, and dont have to break the if-then-else structure (?)
Code:
alias checkvar {
  ; -stuff-
  echo -a START of the if-else statement is reached

  if ($eval($+(%,VariableThatDoesNotExist,$me),2) != $null) {
    echo -a IF  triggers, the var has a value
    ; -stuff with if-
  }

  else {
    echo -a ELSE triggers, the var has no value
    ; -stuff with else-
  }

  echo -a END of the if-else statement is reached (thus no error) 
  ; -stuff that follows, be it if or else above-
}