Today's historic working documents will mostly be SaaS hosted documents in systems like Google Docs, Notion, etc. In the future nobody will be able to open them

Today's historic working documents will mostly be SaaS hosted documents in systems like Google Docs, Notion, etc. In the future nobody will be able to open them. They won't exist, and the software won't exist, and there will be no way to restore it since the software is SaaS that can't be emulated or even installed anywhere.