I don't think it's important who will be left in this scenario (whoever will be last in NPC PID list), it's not a big deal after all. You can "kick" someone and take the right person if you want.But what about if multiple NPCs are just at the same distance to the player? e.g. My Ubersoldat character has CH 6 and leaves Sulik, Vic, and Cassidy outside of SAD. I go into SAD, kill all robots, loot all awesome guns (btw, am I the only one thinks there should be a laser rifle instead of plasma?), and take Skynet with me. At outside I try to "call" NPCs rejoining, but by coincidence they're all at the same distance to me. Now who should be left out? I know that's a stupid scenario, but it can happen.
Question is, does it really make sense having such hot key? In what scenarios you want to leave your party behind except when testing some mods?