Zelda Heart Containers?

I just beat the 8th dungeon on the second quest on The Legend of Zelda for the NES, and I just realized that I only have 15 heart containers. I checked to make sure that I got all five of the secret ones, which I did. So I'm wondering, if I beat a boss and went to grab the triforce piece without picking up the heart container, will the heart container still be there if I go back, or is it gone for good?