As long as you bought quality laminate and installed it correctly, you should not have a problem. If there were any areas where the subfloor was uneven and the laminate was laid over it, you can expect the laminate to warp to those areas, especially under the weight of the piano.
You should use those protectors that go under the legs of furniture to ensure that you don't scuff or scratch the laminate. Also be sure to protect the laminate while moving the paino across it. There is a product called Florguard that can help with this.
Here is a guide that will help you make sure that you purchase quality laminate, if you have not already made your selection. www.findanyfloor.com/BuyingGuides/...
Let me know if you have any more questions