If Jesus did not actually resurrect, then he/she/they (the apostles etc.) soon would have visually seen his remaining corpse.1 This is relevant because they did not see a remaining corpse of Jesus's, but they continued believing Jesus resurrected.
For Jews like the Apostles (and others), mere ostensible visits from a dead person would not be interpreted as a resurrection appearance or suggest that a resurrection had occurred. (After all, a resurrection is a very particular thing in Jewish thought, and other categories of interpretation would much sooner present themselves[Forthcoming]. Something convinced them that this was not a ghost, hallucination, etc.)1.
If Jesus did not resurrect, then he/she/they would have lacked reason to believe that he resurrected. After all, if no Jesus resurrected, then no resurrected Jesus appeared to them, and then there is nothing else left to causally explain their belief that Jesus resurrected.1