does blue Diana still reveal if I don't pay to predict?

No — if you don't pay the [1], none of the effect happens: no Predict, no reveal, no draw.

Diana, Lunari's ability uses a "pay [1] to [Predict], then reveal…" structure — the Predict, reveal, and conditional draw are all linked to the payment. Rule 444.2 makes paying optional, and if you decline, the instruction is ignored and the rest of the effect doesn't execute (FAQ #11290; updated card text via the Vendetta errata keeps this structure). So the reveal only ever happens if you paid the [1].