We will have that the graph for the center of mass will look like:
This is since at the very end the two blocks will keep moving, one with energy that it didn't have before and the other with less energy.
***Summary***
From tA to TB: Block A will be accelerated and thus the center of mass of the system will move towards block B.
From tB to tC: Block A will still move towards block B but at a constant speed, thus the center of mass keeps moving towards block B.
From tC to tD: Block A will still move towards block B but it will decrease its speed due to the rough surface thus the center of mass keeps moving towards B, but slower.
From tD to tE: Block A collides with block B, thus block B starts to move due to conservation of momentum and block A moves slower since some of its energy is transferred to block B, thus the center of mass is now constantly moving and is between blocks A and B.