For how long?  Ultimately, he will die...

Perhaps a better question might be:
"How long will he live?"
Or:
"How long will he remain conscious?"

At that temperature, the water in his body will not remain liquid for
long... Water boils at approximately 10C(=48.2F) on Mars... Now, will
he remain conscious long enough to die from dehydration?  Probably
not... The Martian atmospher is approximately 1/100th as dense as
Earth's... If he only had air and not O2 in the tank, it would result
in a PPO2 of 0.002... Mt. Everest has a pressure of about 1/3rd of sea
level, so even if someone could remain conscious without supplemental
O2 at the top, Mars would be approximately 3% of that... It is
extremely unlikely that someone could remain conscious on this little
O2... With 100% O2, we're now at 15% of the pressure at the top of
Everest... Still rather unlikely that someone would remain conscious
for very long... Long enough to say, "Oh sh.t, beam me back Scotty"?