Welcome to Librarium Online!
Please help me if I am missing something. These two seem to be the same thing, one for I.C.'s and one for everything else. Why the need for two different rules for the same thing? The only difference that I can see is that Ever-living allows a roll even if the squad that the I.C. was attached to was wiped out. Is this the only reason or is there something else I am not seeing? Thanks in advance for the help.
You basically hit it on the nail: Everliving allows an IC to get up, even if an attached squad is wiped out. They probably decided to do it to stop arguments about whether ICs could get back up should the rest of their attached unit be killed.
Also note that RP lets you get back up within coherency of the remaining unit; EL lets you get back up within 3" of the spot you dropped.