A valid B2 with a fixed date shouldn't get cancelled, no matter how long it's been issued or even if it's in an old passport. My girlfriend is not a visa waiver national so has to have a visa, but the 10-year B2 in the passport two passports ago (if you see what I mean) still works for her.
It is true, though, that "indefinite" B2's are now being treated as having expired after 10 years. But I suspect that indefinite visas were probably mostly issued to visa waiver nationals anyway, virtually all of whom simply don't need one any more