[..]Twitch Partners, Twitch Prime and Twitch Turbo users will have their broadcasts saved for 60 days before being deleted. All other broadcasters will have their broadcasts saved for 14 days before they are deleted.[..]

Source: https://help.twitch.tv/s/article/video-on-demand?language=en...

I hope someone made backups. I think are ways to reupload those videos, or make them longer available. I looked at some other streamers archive, and some do have way older videos under the highlights-section available.