A TCP connection would identify the missing packet, and re-request it from the server. Despite the fact that it's still receiving the quake packets, it doesn't pass these on to Quake yet. Because TCP is ordered, it waits until it has a complete stream, exactly as it was sent. The advantage... no packet loss and all packets arrive in the right order! All missing packets are replaced. The disadvantage... a sudden complete lack of packets whilst the missing one is resent.
A UDP connection would continue to send the packets. When quake sees that there are missing packets, it'll put those sexy red lines on your lagometer, and just carry on. It knows it might miss a few packets, and they're not too crucial since it might drop a sound or an item pickup, but whatever happens it will be able to pick up straight away from the next packet. If the lagged / dropped packet ever arrives, it'll just be thrown away because it's out of sequence.