Can you fix oil leak in your car without replacing the engine
Why would you replace an engine to fix an oil leak? Did you mean remove an engine? Where is the oil leak located?
An oil leak is almost surely an indication of leaking gaskets, and while the cost of replacing some gaskets can be pricey, it is definitely a lot cheaper than replacing an engine.
However, then there is the question of how much one should spend to repair a 17 year old car.
How many miles does it have on the odometer?
Has it been maintained at least as well as GM specifies in their maintenance schedule?
Does it have an automatic transmission, and if so–has that transmission been serviced at least 4 times over the years? If the trans has not been serviced every 3-4 years, then it is at or near the end of its life span, and it would be foolish to spend money on repairing an oil leak that would be followed by the need to overhaul the transmission.