For most of human existence, you would already know if Bob or Jane was dead, since you’d have gone to their funeral or knew someone who had.
The problem with this is simply that it’s not absolutely free, and the people promising savings through outsourcing need it to be free to make their promises happen. Cutting budgets everywhere removes the slack you need to deal with things like this.
The possibility of impersonation isn't limited to pension pay-outs but many other things as well. A once-per-year on-site visit would work and would just be a cost-of-business item, and that cost could be lowered substantially by collaborating with other entities who take an interest in such information (banks, governments etc).