Brindle face is killed by Tigerstar to give the dog pack a taste for cat blood Bluestar also dies trying to defend Fireheart from the dog pack and she is thrown off the edge of the gorge along with the pack leader
whiteclaw drowns in a battle
Silverstream.She died of giving birth to Graystripe's kits
Birdflight does not die in a book, but she dies.
Scourge dies in the 6th book of the Original Arc 'The Darkest Hour'.
Honeyfern. but Holly leaf also "dies" though shes still alive hollyleaf does Hollyleaf doesn't die. Just Honeyfern.
In the book "Sunrise" of the Warriors series, Hollyleaf dies after being trapped in a tunnel collapse. She sacrifices herself to save Ivypool and Dovepaw.
If the leader dies in the warrior book series, the deputy would take over. Like, when Bluestar dies--Fireheart was the deputy--Fireheart would take over the leadership of the Clan.
If by ambush you mean the final battle then it is unknown because the book has not come out yet. It is rumored that Firestar dies but it is unknown.
It is out. Book 6 is out too.
Moonrise
So far, Stoneteller, from the tribe of rushing water, dies. That is all that I know so far, although I don't think he dies during the book, but before.
Omen of the Stars Book 5: The Forgotten Warrior comes after Sign of the Moon in the Warriors series.