If a creature blocks and is then bounced before damage, does the attacker deal damage to the player?

Once a creature is declared as a blocker in the Declare Blockers Step, the attacking creature's status becomes 'blocked' — and that status does not change even if the blocking creature later leaves the battlefield. This is established by CR 509.1h: a creature remains blocked for the rest of combat once it has been blocked.

When the blocking creature is bounced (returned to its owner's hand) before the Combat Damage Step, the attacker is still considered blocked. Because there is no longer any creature in its 'blocking' slot, the attacker simply assigns zero combat damage — it does not 'punch through' to the defending player. This follows from CR 510.1c, which states a blocked creature assigns its damage to the creatures blocking it; if none remain, it assigns no damage.

The one major exception is trample (CR 702.19). A trampling attacker may assign damage to the defending player equal to its power minus the minimum lethal damage needed for the now-absent blocker — which, since the blocker is gone, means it can assign all its damage to the player. So trample effectively turns a 'bounce the blocker' trick against the defender.

Example: Your 4/4 Charging Rhino (no trample) attacks. Your opponent blocks with a 1/1 Bird, then casts Unsummon to bounce the Bird before damage. The Rhino is still blocked — it deals no combat damage to your opponent this turn.

Summary: bounce-before-damage saves the blocker but also 'saves' the attacker's damage from reaching the player, unless the attacker has trample.