You have a 50/50 chance of getting either pet back! However, it will combine the talents of the pets, so you have a chance, since you are using a Sea Dragon to get better talents on a Helephant!
However, you can get another Sea Dragon and have a chance at getting worse talents from you Helephant!
Still, if you are looking to improve your Helephant, keep hatching with a Sea Dragon and every time you get a helephant, train it to adult and hatch again! You will eventually get a Helephant with awesome talents!
You will either get another helephant or another sea dragon. However it's potential will be between 52 and whatever the sea dragon has (72?). It's talents might come from either parent.