I think it would depend on their circumstances. If a muggleborn had been on the run all year for example, they would really struggle if they attended school for the last two months, given that they wouldn't have practised magic for the whole year. In that case I think they would be more likely to return in the year, either right away or the following year - because its possible too that they might not immediately hear about the war ending if they were hiding as muggles without any contact with the wizarding world at all.
Those at the ward should be able to go back to Hogwarts and continue with extra help, as would any students who had fled to Beauxbatons (unless they actually chose to stay there and not return to Hogwarts at all).
So I think the best we can say is its a combination of driver's choice and realism for the individual character depending on their circumstances. Sorry I can't be more helpful!
