>>/18781/
Endchan is an imageboard, imageboard content is ephemeral.
Couple of online services are available to archive threads:
https://web.archive.org/save
https://archive.ph/
You can also try simply saving pages File/Save Page As.. and keep an archive on your computer. It can be uploaded to online storage. Or even a VPS can be rented and the files uploaded where one could browse them inactively.