Potentially yes, but in the past I've had well over 50 survive into adulthood in a probably overstocked community tank (including, amonst others, a good few angels). It's really luck of the draw. Easiest thing to do would be to just have male guppies, platies don't reproduce quite as fast, and you could ask at your LFS whether they'd potentially take fish off your hands should they reproduce, I know mine do!