Must a plaintiff physically appear in court for a civil litigation trial?

1) An attorney cannot testify as to facts--it requires someone with personal knowledge to do so. Typically, that is the plaintiff--one could imagine that in business cases, there could be some employee or agent of the plaintiff that would know everything that the plaintiff would have to testify to, and so the plaintiff him/herself would be unnecessary to his/her own case, but that would be the exception, and would not apply in any sort of tort, personal injury, malpractice, etc. case where the plaintiff's own testimony is vital.
2) Of course, even if it was one of those rare cases where the plaintiff could put on his/her own case with the use of other witnesses, the defendant has an absolute right to call the plaintif as a witness and force him/her to appear.
Overally, it is almost impossible to conceive of a case where the plaintiff would not have to testify.
3) Being out of the country is NO grounds to not appear--a judge would find that if it's more important to be out of the country than appear for a lawsuit which the plaintiff, after all, started (it's the plaintiff's case), that's the plaintiffi's choice...the lawsuit will be dismissed and/or a judgment rendered for the defendant if the plaintiff was necessary and did not appear. The plaintiff would have to choose between his/her suit and whatever he/she is doing extraterritorially. If the absence is known in advance, it may be possible to reschedule the trial for when the plaintiff is available, but that can't be done on the eve of trial.
4) IF the plaintiff is disabled to the point where he/she *cannot* appear--e.g. on life support; or actively in the hospital undergoing treatment at that moment--then it is likely that upon proper application, a judge will allow video testimony, though if it looks like the plaintiff could appear in the future, the judge may adjourn or delay the case.