If you did not TALK to the dying guy mission get bugged and you would need to start from scratch.
There is a few ways this can happen.
You enter area and start scanning stuff, guy dies now it can never be completed.
Maybe you went to area but didn't want to do the mission at that time, again guy will die and now mission is bugged.
This might not even be a bug, it might be by design but they forget to fail the mission if you do not talk to the dying guy.
I'm also pretty sure you NEED to talk to dying guy BEFORE scanning or it will also bug out.
I know it's very hard but just really never ever SCAN anything unless stated in mission objectives because it is such a bad game design that if an object is scanned it can't be scanned again for mission updates, this is by far the most idiotic design in any game I ever played before. How this is not fixed even in patch 1.2 can only mean that the code behind is made in such a stupid way it might need a complete rewrite to work as it should have from release.