The essence of it is there's not much happening with sindri after everything wraps up, which makes sense given what he's been through. You can catch him during brok's funeral sequence if you tackle the a viking funeral favor but he's pretty much checked out emotionally and pushes away any attempts to console him. After that point, you won't find him manning the shop anymore since lunda takes over all the smithing duties, and while you might hear characters mention him around places like his house, there aren't any meaningful conversations to be had.

It's actually a pretty deliberate choice that fits the story they're telling, since his withdrawal really drives home the impact of loss and unresolved grief. If you're hoping to find him hanging around for some post-game chats or upgrades, you might be disappointed but honestly, it would feel a bit off if he just bounced back to normal after everything that happened.