So are they Immortal like Zidane?. Also in there coming to Gaia will they eventually get souls or will they just die like the Black Mages. I thought that they would'nt be able to survive long if they had no soul. Due to Gaia' blue light was supposed to cause them severe pain and a soul was needed to not feel Gaia' light.

Zidane's soul was immortal, as he was given a soul of his own; unlike Kuja. So with that, Zidane, Mikoto, and Garland are the only immortals. Garland had ultimate power over them all, but the former two were capable of living extensive lives. Yarly.
The blue light was Gaian, not Terran. It was kept on Terra as a reminder that the assimilation was not complete, and will turn red once the assimilation was complete; "when Gaia becomes Terra." The blue light also signifies Terra's dependence on Gaia to survive.

So...Zidane's soul is immortal?

wow...


Souls cannot be hurted that is why...is it?

well isnt the question if the Genomes were immortal? The question to that would also be no. The souls themselves were immortal, that is the part that the lifa tree holds. Its basiclly the keeper of the souls for when someone passes away and redistrbuites a soul when someone was born. However Garland was using the lifa tree to keep all the souls and only give them to the Genomes when Terra and Gaia once again became one.