No, they will not have to pay back subsidies unless they were given too much, then they have to pay it back.
For example, say someone gets a raise in pay during the month of June but does not let the “marketplace” know about it. At the end of the year, their income is more than what they first reported. And the subsidy was based on their first reported income (which was less).
So, they now owe back to the government the difference of the subsidy (based on original vs. year’s end income).
That’s a shame.