？
Can't we push it back to tomorrow?
Literal
Tomorrow [until-まで] postpone-can-not?
延ばせないの is potential negative + の (explanatory/question particle). The rising intonation implied by の turns this into a casual question — 'can't we postpone it?' ~ないの？ as a question form is softer than plain ~ないか？ and is common in casual speech.