Rust = a death sentence for your blade? Luckily, no.
For minor surface rust, a suitable rust eraser may help, but it is abrasive and can alter some finishes. Just don't go berserk and scrub too hard, because you will scratch the steel.
And another bonus: the rust eraser can also be used to remove rust and stains from pans, gas stoves and even skis and snowboards.
Start gently: Small spots of surface rust are often treatable, but the right method depends on the steel and finish. A rust eraser is abrasive, so use light pressure, test an inconspicuous area where appropriate, and follow the product instructions.
Take extra care with polished, patterned Damascus, and kuro-uchi finishes, which can be scratched or altered by abrasive cleaning. After treating a blade, wash away any residue, dry it completely, and address the moisture that caused the rust in the first place.