If a company’s fort gets destroyed, how do I disband this company? The only disband button I know of is in the fort UI. So, with the fort gone, where can I find a disband button?
私も同じ経験をしました。襲撃が発生したのでタウンホールのUIから住民へ避難指示を実行したのですが、略奪者たちにタウンホールを破壊されました。その後彼らは守備隊に撃退されましたが、タウンホールは破壊されていて、住民への避難指示を解除できませんでした。そのまま時間が過ぎ、住民達は住居に監禁されたままなので、餓死者たちが発生しました。この状況は襲撃が始まる前のセーブにロードして、タウンホールを壊されずに襲撃を終わらせることで解決しました。もしかしたら私が知らないだけでタウンホール以外にも避難指示を解除できるUIがあったのかもしれませんが、私はそれを見つけることができませんでした。
There ought to be a banner for this company somewhere. Find and click on it - you will see there disband button.
I could be wrong but I thought the Town Hall version of the problem was resolved in a recent update; perhaps you had the problem prior to that ?
/
Thanks for your advice 
The problem is that the company had retreated to the fort before it got destroyed. And, when clicking the retreat button the rallying banner disappears. Still, I looked for that banner everywhere on the map but couldn’t find it anywhere…
I’m curious, if the town hall version of the problem has indeed been resolved, where can one find a button to cancel evacuation once the TC is destroyed, then?
There might be a bug. If you dismantled a destroyed barracks but the soldiers remained “stuck” in a “ghost” company, you can recruit new troops - this will cause soldiers that had become detached to be recruited anew.
I reported this error here some time ago: [v1.1.2a] Untied company
Sorry have searched the patch notes and looks like I was mistaken. 
Just rebuild the fort…