They could have argued for a better deal, its not like Garithos could have taken Lordearon by himself. They could have put out the fires of Stratholme, resettle some of human places that were wasted on W3, idk. Its not like the forsaken could not have lasted longer than normal humans.
Thats besides the point, however. Whatever the reality of their situation, the fact remains that the first action of the forsaken as an organization was to betray and put the final nail on the last members of the OG alliance (even if they were *****) and then complain that the rest of humanity didnt trust them.