My thought if you didn't have a GPS was you could say we were diving the so and so wreck and got pushed off by a northern current. It could give some semblance of an idea of where you were, or give a starting point for boats.
Is the lifeline an actual radio too?
Yes. It's the first Nautilus Lifeline model, which people here have been writing as Nautilus Lifeline Radio. It's much bigger than the new model. It has VHF radio, DSC but no AIS, and an LCD display. There are three buttons: green - for chat to a designated channel (which can be changed on the unit itself with v1.02 firmware, the latest), orange - for chat on emergency channel 16 and GPS via DSC, and red - for sending a distress hail with GPS coordinates relayed over DSC for a period of 24 hrs, every 5 minutes.
When I went to Komodo last year, I made considerations between the different type of devices. The liveaboard I had selected only had VHF with DSC, so my choice narrowed directly to this model. It would have come in handy because the dive group I was with did encounter a problem. Due to strong current, we had to surface sooner than expected, which put us in the wrong location for pickup as well (drift dive). We could see the boat tenders, but they weren't looking for us yet. The guide tried waving the DSMB and we all tried whistles, even my DiveAlert, and none of those worked. The guide asked to try my Nautilus Lifeline Radio and it would auto shutoff every time he tried to chat. The device has a user defined battery threshold that will conserve battery for emergency transmissions, which prevents chat mode from working (though I'm not sure turning off is an elegant way to indicate that). Anyway, we ended up having to wait for the boat tenders to finally perk up and look for us.
Lessons I learned:
1. Make sure the battery is charged every night. I didn't think the battery drain was that much so only charged it well before the trip and expected it to last. It does tell the battery life on the LCD display by mV and percent.
2. Test communicating with the boat radio as soon as you come aboard. I had asked for the boat comm channel before arriving and had set the device accordingly, but never tested until /after/ we had the incident I described above.