It happened to me this week when I was making this Vogue maxi dress I just blogged about on SewPassionista by DIANA.
The front top crosses over and I was missing just a bit at the point on the bottom. I made sure that it was the left side that would be deficient because that part would be completely covered by the right bodice piece and proceeded to add some fabric in this way.
I overlapped a piece of fabric making sure I matched the pattern and cut out the left front. It looked like this.