Indeed it will! As you enter a response, you’ll be able to click somewhere else within the Admin Console, or even leave the UserVoice site entirely. Whenever you return, when you click on the ticket you were working on, you’ll see the text that you had previously typed.
Please note that this also applies to a Note that you are adding to a ticket.
This only works within your browser, so if you return to the ticket using a different computer or browser, you unfortunately won’t see your previous text.