try catch はreturn文の中では機能しない

これはNG　（catchできない）

  try
    return has_key(s:, 'disable_str2vimkeybind') ? a:str : lim#str2vimkeybind#str2vimkeybind(a:str)
  catch /E117:/
    let s:disable_str2vimkeybind = 1
    return a:str
  endtry

これならOK　（catchできる）

  try
    let ret = has_key(s:, 'disable_str2vimkeybind') ? a:str : lim#str2vimkeybind#str2vimkeybind(a:str)
    return ret
  catch /E117:/
    let s:disable_str2vimkeybind = 1
    return a:str
  endtry