Is a judge or jury "to assume or presume" testimony not given after
invoking the fifth amendment would have been negative in a civil
trial?
The Fifth Amendment to the U.S. Constitution states in the pertinent part:
No person ... shall be compelled in any criminal case to be a
witness against himself.
The 5th Amendment can be claimed in any context (where there is an actual risk of self-incrimination) as a matter of U.S. Constitutional law. But the evidentiary weight given to a decision to invoke the 5th Amendment in a civil case pending in state court is not controlled by the U.S. Constitution. As a result, this is instead a question of state law, although almost every U.S. state adopts the same rule or a very similar one to the one that New York State (the state where the case referenced in the link in the question is pending).
In New York State, an adverse inference is permitted when the 5th Amendment is invoked in a civil trial. See, e.g., Marine Midland Bank v. John E. Russo Produce Co., Inc., 50 N.Y.2d 31, at 42-43 (1980).
A court may draw an adverse inference against a party who asserts his
Fifth Amendment privilege in a civil matter, because the invocation of
the privilege results in a disadvantage to opposing parties by keeping
them from obtaining information they could otherwise get[.]
SEC v. Susman, 2010 WL 532060, at *5 (S.D.N.Y. Feb. 11, 2010) (internal citation omitted); see also Commodity Futures Trading Comm’n v. Int’s Fin. Servs., 323 F.Supp.2d 482, 505 (S.D.N.Y.2004)(“because Robinson [defendant] asserted his Fifth Amendment privilege … at his deposition, in evaluating the Commission’s [plaintiff] evidence, the court may draw adverse inferences from his silence.”). An adverse inference may “be given significant weight because silence when one would be expected to speak is a powerful persuader.” LiButti v. United States, 178 F.3d 114, 120 (2nd Cir. 1999).
But the decision to draw an adverse inference is in the discretion of the trial judge.
A judge might not make an adverse inference, for example, if the matter upon which the 5th Amendment was invoked is only weakly related to the merits of the case before the judge (e.g. a question about an extra-marital affair in a state where adultery is a crime asked for purposes of showing the lack of credibility of a witness only), or where other evidence strongly suggests that the adverse inference sought from invoking the 5th Amendment with respect to a particular question is not factually accurate (e.g. when another witness has testified without invoking the 5th Amendment to the same factual matter).
The vast majority of the time, however, the trial judge does direct the trier of fact (i.e. the judge in a bench trial or on a motion for summary judgment, and the jury in a jury trial) to make an adverse inference.
