If you no longer have access to your seed phrase then you should definitely move your funds.
@NewEarthRising
How important is it to you to have access to your coins immediately after the firmware upgrade?
In case your Trezor wallet resets itself, can you wait with the recovery until you get your hands on your seed?
If it's not that important to you to have immediate access, I would suggest you do the firmware upgrade without moving your coins elsewhere. You probably wont need the seed anyways. I think I have performed 4 or 5 firmware upgrades. After 1 of those, my device reset itself. The other 3/4 were flawless. So, it can happen occasionally.
On the other hand, if you need access to your coins immediately after the upgrade and you can't wait until you have access to your seed again, you have to create a new wallet on some other client like Electrum. Write down the seed carefully and move a little bit of your coins to it. Make sure it was received. Recover the newly created wallet from seed to ensure it recovers the correct balance and addresses and then transfer the rest. Perform the Trezor firmware upgrade and move the coins back to your hardware wallet.