Here is the order:

All the Republican-appointed Justices voted to allow the purge and all the Democratic-appointed Justices dissented. The argument was that this last minute purge violated the National Voter Registration Act’s ban on systematic cleaning of voting rolls in the 90 days before the election (out of concern of inadvertently removing voters who are actually eligible to vote.) The question was whether this purge was covered by the NVRA.
As I understand it, citizens who are mistakenly purged will have the opportunity to do same day voter registration in Virginia, but I am unsure of these details. (It seems like the purge included many eligible voters who neglected to check a box confirming their citizenship.)
It would have to be a very close race for these numbers to affect an election outcome. But it will have a great effect on those eligible voters who are mistakenly purged from the rolls.
UPDATE: As has been pointed out to me, we cannot confirm this is a party line vote. It is possible that at least one of the Republican-appointed Justices silently sided with the dissenters and did not publicly note it.