On my exchange, the withdraw shows as processed and the destination shows as a valid BTC address - yet the transaction isn't found and the funds aren't in my wallet. It's been 24hrs and still no sign of them.
which exchange? can you tell us your withdrawal transaction id?
what is your trezor wallet address, so we can check on explorer for its transactions
your transaction may still be unconfirmed or your trezor is connected to a node that hasn't seen the tx
Should I abandon hope and treat these funds as lost?
no... relax. if the tx failed, you should see the amount returned to your exchange account balance
bitcoin fund cannot disappeared just like that, blockchain will show you the money trail
it's only a matter of honesty and willingness the involved parties to rectify the problems