  The post-merger product of the first binary neutron star merger event
detected in gravitational waves, GW170817, depends on neutron star equation of
state (EoS) and is not well determined. We generally discuss the constraints
one may pose on the maximum mass of a non-spinning neutron star, $M_{\rm TOV}$,
based on the observations and some EoS-independent universal relations of
rapidly-spinning neutron stars. If the merger product is a black hole after a
brief hypermassive neutron star (HMNS) phase, we derive $M_{\rm TOV} <
2.09^{+0.11}_{-0.09}(^{+0.06}_{-0.04}) M_{\odot}$ at the 2$\sigma$ (1$\sigma$)
level. The cases for a massive neutron star (MNS), either a supra-massive
neutron star (SMNS) or even a stable neutron star (SNS), are also allowed by
the data. We derive $2.09^{+0.11}_{-0.09}(^{+0.06}_{-0.04} M_{\odot}) \leq
M_{\rm TOV}< 2.43^{+0.10}_{-0.08}(^{+0.06}_{-0.04}) M_{\odot}$ for the SMNS
case and $M_{\rm TOV} \geq 2.43^{+0.10}_{-0.08}(^{+0.06}_{-0.04})M_{\odot}$ for
the SNS case, at the $2\sigma$ ($1\sigma$) confidence level. In the MNS cases,
we also discuss the constraints on the neutron star parameters (the dipolar
magnetic field strength at the surface $B_p$ and the ellipticity $\epsilon$)
that affect the spindown history, by considering different MNS survival times,
e.g. 300 s, 1 d, and 155 d after the merger, as suggested by various
observational arguments. We find that once an SMNS is formed, without violating
the EM observational constraints, there always exist a set of ($B_p, \epsilon$)
parameters that allow the SMNS to survive for 300s, 1 d, 155 d, or even longer.
