after the latest start treaty, russia and the us are supposed to limit their strategic arsenals to around 3500 warheads. 

so far, i havent found any source claiming that china has ever had more than 400 warheads, total.  most say around 250. 

assuming perfect accuracy and zero countermeasures, that means a maximum of 250 targets that china can destroy.  most of those targets would be military or industrial centers, with a smattering of major population centers.  plus, plenty of those warshots would be aimed at south korea, japan, probably russia, too.  the chinese and the russians traditionally dont get along particularly well. 

meanwhile, the american counterforce strike would reduce that by a large margin.  for the birds that actually get aloft, well, the american abm program is pretty damned good. 

china does have up to six ssbs, submarines with icbms.  im really not worried about those, since im sure each of them has at least one attack sub sitting on it at all times.  if they tried to launch, expect them to be sunk before the last missile leaves its silo. 

all in all, the nuclear threat is fairly small, especially considering what it once was.  the only significant nuclear arsenal, other than the us, is russia, and they are even more afraid of m.a.d. than we are.  a nuclear war in the modern age would be messy, sure, but probably survivable.  for most.