if a species is dying more or less of natures own accord, then let em die.
if, however, a species is dying because we fucked something up, then in the interest of keeping earth's ecosystem in check and not being massive assholes we should try to get them back on their feet.
as for the pandas, were not even helping them as it is. we're just keeping them in what is effectively life support; they cant really live without our help, and we really cant do much to get them to survive on their own short of tearing down everything we've built in their habitats. sad as it makes me, the panda cant really be saved even if we wanted to do so; they just dont have the desire to breed anymore, and if youve lost that, what the hell can you do about future generations?
all the more reason we need to get going on the space program; so we can find some aliens who can breed pandas....and cure cancer or whatever, but mostly save the pandas.