Here today, gone tomorrow is an expression for something that is short-lived, fleeting, lack permanence, or something that is present/exists only for a short time. For that statement to be precise, you can replace the expression "here today, gone tomorrow" by any of the meaning stated above. Example - Fashion fads exist only for a short while. Fashion fads are fleeting. Fashion fads lack permanence in the market. In this way, the meaning of the sentence is more direct.