Have all of the 1898 Proof Half Dollars survived? One might get that impression from the number of Proofs that have been certified by PCGS and NGC. PCGS alone has certified almost half the original mintage; NGC has certified over 260. That leaves just over 100 ungraded examples. Even if one discounts for resubmissions, this is a large percentage of survivors. Overall quality hovers around the PR63 to PR64 level, though there are some impaired examples at the lower end and some superb Gems at the high end. The finest examples top out at PR68.
At least a fourth, and possibly half, of the 1898 Proof Half Dollars qualify as Cameos. A much smaller percentage show as Deep Cameos -- these are the first coins from the dies.