Last time Leeroy joined them on stage was for a one off during the Their Law Tour in 2005, which celebrated their 15th anniversary. He jumped on stage for a track or 2. Apparently Liam really wanted Leeroy to come back after that night, but Leeroy turned him down and felt that one night was enough. I do think he may be involved in some form with the next album era. Leeroy has been producing music on his own for a while now.
https://leeroythornhill.bandcamp.com