Team Liquid qualified just after ANNOUNCING Dimasick, doesn't mean they didn't practiced with him before the announcement. The rumors of Dimasick joining Liquid were running around for weeks so they probably were practicing together right after Dreamas left, same as they did with Nivera who practiced for months with the team before he was officially announced.
If nAts joins FNC either he learns the Initiator role from scratch, or Boaster moves to Initiator so nAts can stay on smokes, in which case, Boaster would need to learn more initiator agents other than Kayo. Either way, 2 weeks isn't enough for a team to make such a move. It just isn't smart.