In Heart of the Swarm, between two of the campaign missions, I had a choice to head towards two different planets. On one of them, I can unlock Roaches and Hydralisks, on the other, two other units.
I chose the Ice world (Roach/Hydra) without really thinking, but I then thought perhaps I'd like to change. I remember in Wings of Liberty, when given the choice between two missions, the second one would still be there when you completed the first.
Is this the same in Heart of the Swarm? After I complete the Ice world, can I still get to the other (lava) world?