As UNSC Jon 117 says, these connectors are worryingly prone to pop off if there's any movement of the drives. Fortunately they're accessible even after refitting the antenna plate, so I would wait until then for a last-minute check. I've done this job three times now on the same Mac and everything has been fine.
The thickness of your hard drive or SSD plays a part here, I think. With a thicker SSD (Crucial M4) in the upper slot I found the antenna plate very hard to re-install. After replacing this with a Samsung Evo 850 it was much easier, I think because the lower drive has more room to breathe. With the thinner SSD I didn't have to remove the power supply, either – a major plus.
TerribleHacker: "pull it out parallel to the logic board" – no, or at least not on mine. The pins are vertical and the socket has two vertical tongues that fit into grooves on the plug. Vertical is the way to go. In cases like this I use tweezers to pull gently on the wires, and if possible the plug – but the latter is very difficult in this case.