We don't know how he died but in the ultimate guide the new warrior cats book he gives bramblestar a life and talks about how he is in his own little starclan and things

RIP
RAVENPAW
INTO THE WILD-THE ULTIMATE GUIDE
You gave the courge to some to fight the evil

2448114 No! Ravenpaw was one of my favourite cats! *sniff sniff*

2448114 ah yes the ultimate guide. and NOOOO RAVENPAW HE WAS ONE OF MY TOP TEN FAVORITE CATS WHYYYYYYYY

2448738 rage.

He can reunite with Firestar in Starclan now.

2449667
That's a nice way to put it.

let us all have a moment of silence for our favorite loner.

were gonna miss ya, Ravenpaw

2448114 AHHHHHHHHHHH SPOILERS XD