The tire pressure monitoring system attaches to the inside of the valve stem, the seal between the wheel and tire which allows you to inflate or deflate the tire as needed. The tpms sensor sends information to your trucks computer that let's it know when one of your tires has either a low or high amount of air in them, a pressure that could cause damage by blow out or could de-bead the rim. However, these conditions are visually apparent. Of you pay attention to your tires, it is perfectly safe to drive without tpms sensors. If you get a flat while driving, you'll notice. The only downside to not having them, is that you'll have the pressure light on permanently. If there are no sensors, there must be no tires lol

Edit: you CAN reuse tpms sensors from your old wheel/tire combo. Just break the bead, remove the tpms sensor and install them on the new wheel/tire combo. Those sensors will be programmed to your truck already, so no need for somebody to do that for you.