2004 Lexus ES 330 Replacing pads without rotors

My car has 113,000 and I have never had any type of brake work done until now. I know I need new pads because they are down to the indicators. The rotors cannot be turned because they are too thin but are apparently still within spec. I had the garage just put the new pads on to save some money (have been out of work for several months, not just trying to be cheap). Is there and harm in doing this? How will I be able to tell when the rotors actually need replaced? I suspect it will be before the pads wear down that thin. Am I being penny wise and pound foolish? Finally, are there any safety issues by not replacing the rotors at this time? Thanks!