Enter the ruins of Freddy Fazbear's Mega Pizzaplex in the FREE story DLC for Five Nights at Freddy’s: Security Breach! Gregory is once again trapped in the now abandoned Pizzaplex, and he needs your help! Play as Cassie, Gregory’s best friend, Faz-fanatic, and would-be savior as she braves the dark, dreary, and dilapidated pizzeria.

I believe what Gregory was saying before being cut off was he was going to reactivate MXES. He would be apologizing to her because MXES would also target Cassie. From Gregory’s perspective, reactivating MXES might stop the Mimic, as it is designed to keep it from being freed.