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The alleged victim may or may not be needed at the pretrial, depending on what issues are being heard at the pretrial. Pretrial has to do with issues of admissibility, exclusion, etc... and if the testimony
of the "victim" is not something that is being challenged on these procedural grounds (or even if it is but the actual testimony is not being examined) then the victim need not be present. The only requirement constitutionally is that the accused needs to be able to confront his/her accuser at trial. Even in a situation where the victim is not found, the accuser may be medical professionals, police, etc... that could still establish the elements of a crime without testimony of the "victim" (just think about how murder cases would work if the victim had to testify).
The point is that pretrials are usually procedural, and the intent is to make the trial run more smoothly and quickly. It's rare that witnesses need to be there.
Hearsay is a different matter, in that generally speaking hearsay is to be excluded. There are exceptions to this (you can read about at the following website: http://www.shouselaw.com/hearsay.html). The point is that the general rule is that hearsay is to be excluded, but there are a number of exceptions to this rule, and if the judge is convinced that one of these exceptions applies, he/she could allow the hearsay.
In short, the answer is that the "victim" can still show up to trial, but one of the parties to the action (the prosecutor or the defense) still has to "call" the "victim" to the stand. The "victim" cannot demand to be heard if neither of the parties wants to call him/her to the stand.
Hope that clears things up a bit. If you have any other questions, please let me know. If not, and you have not yet, please rate my answer AND press the "submit" button, if applicable. Please note that I don't get any credit for my answer unless and until you rate it a 3, 4, 5 (good or better). Thank you, ***** ***** luck to you!