According to Wikipedia there are a few in uncontrolled orbits, so they might be around for a while yet. As for the ones still under control, it looks like they'

According to Wikipedia there are a few in uncontrolled orbits, so they might be around for a while yet. As for the ones still under control, it looks like they'll drop 15-20km below their replacements as a contingency for a little while, before finally being de-orbited (I can't find any details on the timing for this)