If they gave more time than just a few months, in example at least an entire year, then people could at least download those files before hand. Not sure how long this would take and how stressful this would be for their servers.

They could also give the option to pay for this. They should know what storing a video costs and therefore could give creators the chance to cover that cost.

You should at least play around with the export options and do regular exports. You really don’t want your diary of over 5 years to be stuck in an unmaintained app. And since this seems to be supporting exporting into markdown - maybe try an export and checkout logseq or Obsidian?