Time and again I keep being impressed with your selfless commitment to building and sharing things in the most humane and long-term way. A beautiful example to set, thanks.
And yet they haven't open sourced the app. That would be truly humane and long-term. As it is, it's just another proprietary app that, if it dies, can't be continued by the community.
I don't think monetary issues should be a concern with open sourcing the app - companies like Bitwarden, Gitlab, and New Vector (the company behind Matrix) are doing just fine with their open source products.
The jury is still out on "companies like Bitwarden, Gitlab, and New Vector". Kudos to them for pioneering novel business models.
Your data isn't locked up in a format. Just use logseq or something if obsidian disappears.
Those who write the code have the right to control its source code. They aren't "inhumane" or thinking "short-term" just because its not open source.