Here is an answer from or Forestry Professor, Dr. Pete Schaefer.
If the furniture is made from Sequoia, then it is redwood, which is not endangered. While the number/acreage of very old trees is likely declining, I suspect that the 2nd and 3rd growth stands are stable.
Redwood is excellent for outdoor use. I would not have any qualms about buying it, other than it can be pricey.
Sequoiadendron (giant sequoia) on the other hand is in somewhat of a threatened state. Mostly (as I understand it) due to the lack of fire over the past century, which has allowed much heavier growth of competing firs, pines, etc., and reduced giant sequoia regeneration. Now when a fire gets going in those forests, there is lots of fuel at all canopy levels (“ladder” fuels), which leads to very hot fires that can get into the crowns of the giant sequoias and kill them.