Can the Supreme Court function with eight justices?

There is no requirement to fill a vacant seat as soon as possible. In 2016, Mitch McConnell refused to hold a vote on nominee Merrick Garland after Justice Scalia died. The court was down to eight members for 14 months until Neil Gorsuch was confirmed in April 2017.

P.S. In the event of a tie, the decision of the lower court stands.