In Mass Effect 3 I've missed the meeting in hospital with Thane and now the Salarian Councillor is dead. What should I change with the Gibbed Save Editor to save him? I didn't romance him.
There is no way for you to simply "change his fate" with the save editor I believe. It does not matter anyway, the only thing he would do if he was alive was:
Save the councilor and die after you meet him and his son at the hospital
No matter if you romanced him or not, the only way to change his fate is through the ThaneMOD.