Board Thread:Warhammer 40k General Discussion/@comment-6767898-20130227013545/@comment-6078851-20130406175706

.....when they come back there's a distinct possibility they will be rendered ineffectual (physically, not counting the morale boost) through the bureacratic quagmire they would find themselves in.

the lords of terra will not see their return as welcome as they are likely to want to make big changes, and will feel threatened that their own positions of power may be lost to the primarchs. the inquisition will question their motives for being m.i.a for 10 millenia - not to mention that they could simply be named traitors, one and all, for abandoning the empire.