What happened to Graystripe after Silverstream died?

When Leafpaw, Mistyfoot, and other cats were trapped in the Twoleg cages, some of the cats from ThunderClan staged a rescue mission. The last cat to be rescued was Brightheart. Graystripe saved her, but the van door shut on him before he could jump out. This scene is shown in great detail in 'The Lost Warrior' (Manga #1)