As has been pointed out, a diesel pump is a full 1/4" wider. It would take serious determination to misfuel a gas car with one.
If it did happen, I believe you'd be OK with draining the tank and refilling with gas, and what little is left in the lines would be diluted without much hassle.
If you put gas into a modern CR diesel like mine, it can grenade the high pressure fuel pump and send metal shards through the whole fuel system.
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