Everything gets disabled and there is no way to re-enable it.
Same here, I had to close my server WITH people on it!
It’s possible to re-enable it by clicking on the input part of the chatbox, but it’s hard to do since the cursor’s invisible. If you alt-tab into a non-maximized window and then bring it near the chatbox, you should be able to do so fairly easily.
Thanks for your report! This has been forwarded straight to our Trello board. You can track its status there (it takes a couple minutes to show up on Trello).