Each State has it's own challenging processes. Early voting has almost no challenging process because the voter was alive when voting, but absentee ballots can be cross checked against public records which would make a vote voided. I can't speak to the State of Michigan's process, but my local election boards do remove the deceased. My district has about 60,000 registered voters broken down into 45 voting wards so we are only examining 1500 votes per ward if everyone votes. This is done quite easily in 13 hr vote counting day.