The solution is simple: Remove the dagger mid-combat.

You could make the dagger too hot to hold and it falls out of reach (off a mountain, into rushing water, etc…)

You could make the dagger dissolve away (through lava, acid, being eaten, etc…)

You could make something take the dagger (disarming, stealing, etc…)

A hag/genie/etc could place a curse on the PC (holding anything makes them experience immense pain and drop what they’re holding, anything dagger they hold is turned into a spoon, etc…)

Also, you can buy Tic Tacs from any newsagent or gas station.