NOW LISTEN
I have no idea if this has been said before but anyway. As we know Grantaire was sleeping during the whole fight at the barricade but he woke up the moment Enjolras was ready to be shot to death and died with him. So, what if Grantaire sleeping and then waking at the right time was a parallelism with the people of Paris? We can easily reach to that conclusion considering the uprising of 1848. Like Grantaire, the people may not have been present during the June Rebellion but they actually rose when they felt the time was right. Grantaire was not there in the fight, but rose only when his instinct told him it was the right time. And Enjolras saw it. He saw that despite doubt and despair, in the end there would always be hope. And he smiled before he died, not only because Grantaire had finally joined the cause, but also because he would not be the last one to do so.