  It is noted that a set of facts points to the relevance in four dimensions of
conventional supersymmetric unification based on minimally a string-unified
G(224)-symmetry, or maximally SO(10). These include: (i) the observed family-
structure, (ii) quantization of electric charge, (iii) meeting of the three
gauge couplings, (iv) neutrino oscillations [in particular the value of $\Delta
m^2(\nu_\mu-\nu_\tau)$, suggested by SuperK], (v) the intricate pattern of the
masses and mixings of the fermions, including the smallness of $V_{cb}$ and the
largeness of $\theta^{osc}_{\nu_{\mu}\nu_{\tau}}$, and (vi) the need for B-L as
a generator to implement baryogenesis (via lepto-genesis). A concrete proposal
is presented within a predictive SO(10)/G(224)-framework that successfully
describes the masses and mixings of all fermions, including the neutrinos -
with eight predictions, all in agreement with observation. Within this
framework, a systematic study of proton decay is carried out, which (a) pays
special attention to its dependence on the fermion masses, (b) limits the
threshold corrections so as to preserve natural coupling unification, and (c)
uses recently improved values of the matrix element and renormalization
effects. Allowing for both MSSM and its proposed variant, the so-called ESSM,
as effective low-energy theories, the study shows that a conservative upper
limit on the proton lifetime is about (1/3 - 2)$\times 10^{34}$ years, with
$\bar{\nu}K^{+}$ being the dominant decay mode, and quite possibly
$\mu^{+}K^{0}$ and $e^+\pi^0$ being prominent. This in turn strongly suggests
that an improvement in the current sensitivity by a factor of five to ten ought
to reveal proton decay. For comparison, some alternatives to the conven- tional
approach to unification pursued here are mentioned at the end.
