When you're in treatment, one of the MAIN things they force is that if you want to stay sober, you ABSOLUTELY CANNOT be around others who are drinking. They tell you not to hang around your drinking friends EVER AT ALL. The other members of In Flames ALL DRINK so if Jesper returns to the band, he'll be around all of that and I highly doubt that all 4 other members will completely stop drinking around him which would be the only way for him to avoid the temptation to start drinking again. Well, the very best of luck to him anyway!