Nobody knows for sure.
In a directly relevant case of using Einstein's image, in the case of Hebrew University of Jerusalem v. General Motors LLC, 903 F. Supp. 2d 932,
the Court concludes that the New Jersey Supreme Court would likely
find that the postmortem right of publicity endures for no more than
50 years after death.
That case was decided in California (US District Court), but Einstein's property rights are defined by NJ law, which is where he died. This summary of right of publicity under New Jersey common law (there is no statute) addresses the question from an NJ perspective, and does not provide any definite answer.
One question relevant to New Jersey, arising from Estate of Elvis Presley v. Russen, 513 F. Supp. 1339, is whether Einstein's persona was exploited during his lifetime. If so, then following the precedent of the Presley case, Einstein's personality rights survive his death. If not, we don't know. The Presley court left that outcome undecided:
we "need not, and therefore do not, decide whether the right would
survive the death of the celebrity if not exploited during the
celebrity's life" since Presley exercised the right to commercially
exploit his name and likeness during his life.
(quoting another Presley case, Factors Etc., Inc. v. Pro Arts, Inc., 579 F.2d 215).
As for the duration of such a right, the court also declined to decide:
Since we are not directly faced with the issue of whether there should
be a durational limit on the right of publicity after it is inherited,
we will not decide this question. However, the court suggests that a
length of time should be set by the New Jersey State legislature. The
Federal Copyright Act, 17 U.S.C. §§ 302, 305 provides guidelines which
may be informative in this situation.
This suggestion (50 years at the time) seems to encourage the later GM court in arriving at the 50 year figure, rejecting the argument of Hebrew University for 70 years.
In the GM case in California, that court states that
Nothing in Albert Einstein's will specifically mentioned any right of
publicity, and during his lifetime he did not claim or receive any
monetary compensation for the use of his persona
Applying New Jersey law (because Einstein was domiciled there at the
time of his death in 1955), this Court concluded that New Jersey would
recognize a common law postmortem right of publicity without the
requirement of lifetime exploitation.
which is not exactly what the Presley court decided.
That court then concludes that it must determine
whether he would have intended to transfer that right to HUJ through a
provision in his will
The GM court reasons that
unless sound public policy and the weight of authority establish
otherwise, it makes no sense to apply the California statute's 70 year
postmortem durational limit—which is part and parcel of the
substantive right—to a right arising solely out of the New Jersey
common law, and there is no legal principle requiring this Court to do
Still, there isn't a compelling argument for 50 years.
So in summary, it is undetermined whether Einstein would have intended his right of publicity to be inherited, or whether NJ law creates such a right post-mortem. It is pretty much guaranteed that HUJ will mount a powerful legal attack.