Yes, it will be difficult for Levarlet to cope with this even if he was sober; if he was drunk it will be even harder. One only has to look at how long it has taken Beñat Intxausti to come to terms with the death of Xavier Tondó, an incident in which he was a blameless party who just happened to be the one who was there at the time of the accident. He said that you always feel that there was something you could have - should have - done differently that could have - would have - changed things.
I will preface this by saying that I have not seen the accident that cost Isaac Gálvez his life and led to de Fauw's suicide, but those I know who have have said it was a racing incident; perhaps de Fauw was at fault but it was just something that happens in cycling and this time with tragic results. And it took him three years of struggling to cope with it before his death. So there, he will always again think of things he could have done differently, but it was just something that unfortunately happens in the course of being a professional. For Levarlet - as with Claveyrolat - things will be even tougher to come to terms with, because there isn't that aspect to it, and he can't be comforted in that way. Yes, these things happen, but he will always feel directly responsible.