Grantaire notices that flash, of course-- there's very little he doesn't notice about Enjolras-- and places it pretty easily. Enjolras was the leader, after all. And furthermore, he's here and they aren't. It makes every bit of sense, and he has no intention of commenting on it.

"There's no easy beginning, of course. Probably not an easy middle, either." The end, though, the end he knows by heart. "Just... whatever strikes you, whenever it strikes you. Whether it's in five seconds or in five weeks. I won't be going anywhere, Enjolras." His voice turns a bit wry as he adds, "I know I'm not the most reliable. But at least it's this place making the promise for me, so you can probably at least count on whatever it is that's keeping us here."