you can't decrypt without a ticket (or more exactly, without the encrypted title key located inside the ticket file)
The ticket is provided with game updates, because updates are free. so nintendo provides a ticket for free along the downloaded update. The ticket is tied to that update, you can't use the same ticket for another title.
If you download the full game, don't expect nintendo to provide the ticket for you if you didn't pay for the game.
But the title.tik content is not needed to decrypt the downloaded files (update, or full games). You only need the encrypted key linked to the file you want to decrypt.
create a file or edit any file in hexeditor and place the key at 0x1bf (if you know the key)
it's not necessarily a title.tik file that you need, could be "random_name.ext" with the key at 0x1bf and it will work too.
example to generate an empty file with the key at the correct position with python
Code:
python -c "import binascii; open('title.tik', 'wb').write(b'\0'*0x1bf + binascii.unhexlify('<pasteyourkeyhereinbetweenthequotes>'.replace(' ','')))"