my timing belt is wearing [cracking]. what happens if it breaks

Hello! Which engine do you have? The 4 cylinder or the V6? If it's the 4 cylinder, it's what's called a "non-interference" engine, meaning if the belt breaks the engine will simply stop running, without breaking anything internal to the engine. If it's a V6, same deal, unless it has VVT-i (easiest way to check is to see if the engine cover says this in big letters), then it can bend valves if the timing belt brakes. Service interval on the belt is 60k miles. With all of that said, how do you know your timing belt is cracking? It's not visible from looking in the engine bay without taking off the engine's front cover. Perhaps you mean the serpentine belt that runs the accessories (alternator, AC, pwr steering). This is not nearly as vital and much cheaper to replace. If it does break, you would lose power steering assist, as well as the alternator charging.

If your Toyota engine has a timing belt it is a non interfereance engine. Period