In any case in which the issuer spends the promised coins(the used UTXOs in particular transaction) in a counter-promising manner, the creditor will send the GT to Bitcoin network. So the miner will face two different transaction which are using same UTXOs as input. Which one the miner will chose is up to the transaction fee. That is the point of Sabu protocol. The Guarantee transaction (GT) has a far higher transaction fee comparing the Main transaction. Indeed the GT cuts a portion of issuers and creditors money and dedicates it to miner transaction fee. So in 99 % of times miners will put the GT transaction in next block instead of MT. If a creditor send the GT to Bitcoin network he will lose a portion of his money as well as issuer, but this lost is less than what he lose if issuer cheat him.
So, what happens if I send a transaction of 1BTC with a fee of 0.99 BTC?
I will be a bad creditor but at the same time, all the money is lost, so who will cover for this loss?
Also, as far as I understand the creditor will only give you access to the UTXO that covers the amount in the SABU protocol, it's all nice in your models to overcome an "evil" creditor but you have only counted a simple tx, not if he plans to combine inputs and use it to pay to different outputs, he will have another fee advantage over you as as a 1input, 2 outputs tx is 180 bytes and a 2 in / 10 out is 552 bytes so he will outbid you and still manage to save on the fees for the other transactions he was supposed to do.
And now to the SABU protocol, it's a centralized system, right?