Back in May, Microsoft announced that Cortana—the Windows digital voice assistant, not Master Chief's original AI ladyfriend—was being deprecated. Which is a word from the Corporate alignment tongue that translates into English as "killed off".
Her replacement is Windows Copilot, an AI-based personal assistant that does similar things but with a generative language model and less personality. Copilot can answer questions about Windows, summarize documents, suggest Spotify playlists, and so on. There's also Bing Chat as well, I suppose.
Assuming you haven't already disabled Cortana, she won't actually die unless you apply the latest Windows 11 update. If you do, she'll no longer be accessible on your PC, joining Clippy on the scrapheap of discarded Microsoft assistants.
There's one small note of hope for people who get sad about robots dying, however. In the End of support for Cortana in Windows and Teams article on Microsoft Support, there's a note that "Cortana in Outlook mobile will continue to be available." I didn't even know there was an Outlook app for mobile, but apparently there is, and Cortana will live on within it as a disembodied voice that reads your email out loud, and definitely won't ever go rampant and attempt to awaken ancient constructs left behind by a lost forerunner species.
