Must he do anything for the present, or can he simply leave things for his successor (if he is confident that the next POTUS will be Hillary or Bernie)?
OTOH, if he and his team believe there’s a significant chance of a Republican victory, they would probably want to nominate someone right away. What delaying tactics could the Republicans use? Is there a time limit or some other ‘rule’ that compels an appointment be made to the SCOTUS to replace a justice who’s died (or incapacitated etc.)
In the meanwhile, with Scalia out of the equation, it would seem that the balance on the Court has shifted leftward. And, critically, until Scalia has been replaced, the likelihood of a ‘liberal’ majority to prevail in any given case has increased markedly. So, even if the Republicans delay things, we will still see a (potentially very short-lived) liberal regime on SCOTUS.