Upsie daisy, that would be silly thing to do...hypothetically of course..
Well..if it would be my hubby who would have indulged his curiosity towards iron...and managed to ruin our best pillow cases...
....I would first give him wet towel around ear hole and send him away to dig alloment....no, weeding is better punishment
Then I would put hot water with drop of vinegar added into bottom of the bucket..just a thin layer so that only bottom of the hot plate is under water..and eventually starting to rub with finger or spunge and see if it comes off..if not...another soak with washing up liquid added...if not...then its is time for WD40 and rag option...and if not even then, then it is time for 'send hubby to buy new one with his weekly allowance' treatment...that should sort it out.
I bet you realized there is nothing you can do to the pillowcase..other make it disappear and hope that nobody will notice..