It's not reliability we're talking about, it's about durability. For reference, S3 has eleven 9s of durability.

Every major queuing system solves this problem. RabbitMQ uses unacknowledged messages which are pinned to a tcp connection, so when that connection drops before acknowledging them they get picked up by another worker. SQS uses visibility timeouts, where if the message hasn't been successfully processed within a time frame it's made available to other workers. Sidekiq free edition chooses not to solve it. And that's a fine stance for a free product, but just one I wish was made clearer.