I've been to a few similar nights and seen a few guys completely choke when they get up there, was probably worse than 5 mins of bad material. The audience is sympathetic though and talking or heckling is frowned upon so I should be alright as long as I remember my material under pressure.
Yeah, he's a genius for improvised stuff and going off on a tangent. You've got to remember though, he's been doing stand up since he was 15, it took him some time to develop.