Atrial contraction in complete SA block
It depends.

It's likely that another point starts setting the pace instead of the SA node. More infos about cardiac pacing on Wikipedia

Or maybe different points try to set the pace contemporary, without generating a valid contraction but only electrical activity (such as in atrial fibrillation/AF, a very common disease mostly in elders).

An electrocardiogram could answer the question for the specific patient. If there is completely no atrial activity you'll find no P waves (no atrial activity) or baseline continuous little waves (in case of AF because of the irregular atrial activity) and probably bradycardia (because the pacer in the AV node is slower than the SA node).