He'll still be grouchy about it but ultimately understanding, and offer to assist in any way he can, if the research ever needs someone who's good at punching cutting things or going further into the segments. He'll express similar hopes even if he knows the chances aren't big -- has anyone came back after disappearing so far? -- and will probably spend some time with Helene to talk about Hange, as she probably knew them fairly well by now, too. Can he buy you a terrible rainbow drink, Helene-

He'll also be touched by the immediate agreement and might even thank her. It won't bring Hange back but like this at least more people will hear their name and remember them for what they loved doing.