As Texases said; a timing belt breaking on the V-6 motor will cause valves to hit pistons. But even if this happens; it is not a sure thing that the whole engine will have to be replaced. If the cylinder heads are removed and the pistons are found to not be damaged; then the engine can often be repaired by installing new valves, checking the valve guides, regrinding the valve seats, and installing a new timing belt and associated components. Unless an experienced mechanic tells you that Saturn V-6s always break pistons when the timing belt fails; I would consider removing the cylinder heads and checking for damage.
Of course; it would also be worth investigating the cost of installing a used engine; compared to the unknown expenses of trying to repair this one.
If your car has the 4 cylinder motor; the valves cannot strike the pistons when the timing drive fails. Only the V-6 is an interference engine. The 4 cylinder Saturn motor is NOT an interference engine; and the valves will not be damaged if the timing drive fails. The 4 cylinder Saturn motor has a timing chain; not a belt; but the chain can eventually stretch and fail, just like a belt does.
But your description of the engine cranking really slowly does not match what usually happens when the timing drive goes out. The starter in an engine has to overcome the compression to turn the motor over. When the timing drive fails; there will be much less compression in the cylinders; so the starter will spin the engine faster than it usually does. If your starter is really cranking slower than normal; and you are not confusing the starter cranking speed with the cranking speed when the cylinders start firing (which is of course faster than when the starter runs without the engine firing); then it sounds to me like something else has happened to the motor.
There are many things which could happen to an engine that would make it stop and then crank more slowly. One would be a blown head gasket that let coolant fill the cylinders. Another would be that it ran out of oil, and the pistons or bearings were damaged. A defective crankshaft position sensor could also do this.
The first thing I would do to sort this out is to check the engine oil level. If there is no oil on the dipstick; the engine ran out of oil and is probably ruined. If the oil level is OK, and there is no foam or water bubbles in the oil; check the radiator coolant level; by removing the radiator cap (NOT BY JUST LOOKING AT THE RESERVOIR LEVEL).
If the radiator level is very low; the head gasket may have blown. In that case; I would run a compression check on all the cylinders. If all the cylinders have compression of more than 150 psi; then the timing chain has not broken or jumped out of position. But if all pressures are above 150; and one or more cylinders have 40 or more psi than the other cylinders, the head gasket is probably blown. The spark plug in the cylinder with the extremely high compression will probably be soaked with coolant; and a bunch of coolant will be blown out of the spark plug opening when you crank the motor with all the plugs removed. The engine will crank very fast after the coolant has been blown out of the cylinder. If that happens; the cylinder head will have to be removed, and inspected by a machine shop for cracks, damage, or warping. The head will either have to be remachined or replaced, and a new head gasket installed upon reassembly.
If the compression is good and even in all cylinders; and the oil and coolant levels are good; I would check for spark and fuel. This may be more than you could do yourself; I would suggest not going back to the technician who told you that the 4 cylinder Saturn is an inteference engine. It would also be fair for him to refund the amount you paid him for the bad information he gave you.