If you are using Nokian or Schwalbe studded tyres, the studs will probably outlast the tyre. As far as I know, only Nokian and in the last couple of years, Schwalbe use Carbide studs. I think all other...I should probably say MOST others...use more common steel studs. Those wear out quickly.
I've been running Nokians in the winter for several years, and they still look like new...BUT...I don't run them all winter. I have them on a second set of wheels, and used to put them on the bike only on crappy days. Now, I have a second commuter bike for crappy weather, and leave the tyres on all winter, but only ride that bike on crappy days.