I lost my left big toenail the first time about 3-4 years ago. I dropped a piece of pipe on it. Even though it never showed any bruising, a couple of days later I could tell that it was separating. I didn't lose the entire nail, just everything but 1/4" or so. It took months to grow back, was painful after walking a lot and I lost it again.
The second time it came back, it was slightly discolored and has been ever since. I went to a podiatrist and was informed that the discoloration can be either directly from the trauma or from a fungus. If yours stays discolored, they can take a sample to check.
Through the process I thought the same thing, that I was going to end up with a very short toenail, even the second time. It grew back completely both times.