L1a visa and stamping date difference

I and my family have L1a-visafor three years. But my visa entry work authorization ends in 2 years. My wife is expecting a baby and she wants to deliver the baby here in US. Can she stay back in US though my work authorization ends now but Visa still remains valid fir one more year. She is on L2 dependent Visa.

No, she cannot stay. Her status is dependent on yours. If your work authorization ends now, so does her stay too. Visa stamp is just to gain entry into USA, but does not provide any legality to stay here in USA.