I really want to use Li'l Devil and the Katana for my crit build but Mick bugged out on me and couldn't even access his merchandise menu. So I figured that killing him will transfer the GRA content to Vendortron after 3 in-game days have passed.

So I waited....
and waited...
and waited...

One month passed in-game and not a change in the Vendortron's merchandise list.

Like my title suggests, how long again?

It won't, I believe. The Vendortron will stock the merchandise if GRA is downloaded, etc and the people stocking things are already dead, but it doesn't update to reflect when someone dies AFTER the add-on takes effect.

I did the same thing with a few merchants. I was less than pleased.

I rather disliked Lil' Devil if it's any consolation.

I was so mad that I started a new game and Mick's inventory menu didn't bug out on me.

I haven't tried Li'L Devil yet but the Katana is definitely putting in work. And I have no mods equipped for it at the moment.

I like Lil' Devil, in my opinion it shares the category of hand cannon with the Ranger Sequoia with slightly easier to find ammo and a higher reload rate.