I recorded a minute's worth of heavy traffic with tcpdump.
The resulting pcap file was ~8GB. I then processed the file using:
The machine, a c4.8xlarge, had 64GB of memory, about 55GB of the which showed free using top when the mongoreplay record command was run. Little by little, free memory declined until the process crashed with:
Link to the pcap file and full mongoreplay output from crash in first comment.