I am in Europe and I would not trust that SEPA transfers are irreversible at all. There are cases every few weeks in the German subforum that support this claim. Even if they are irreversible, your bank account still will get locked up sooner or later as soon as someone sends you money from a phished account.

You just describe NashX and as I already said, there are strategies where Bob can benefit from Alice loosing money, even if it costs him a bit as well.

Once the collateral gets higher by the way, there is an easy extortion attack: freeze both collaterals + Alice's coins she sells, don't send money but agree to release the collaterals at least if she claims to have received money. As soon as the collateral become worth more than what she would have gained from selling the coin back in the days, she is acting economically rational to agree to that deal.