Possible Clues:

• Nonappearance of Norwegian playwright beheaded in a church
• Leo, non-starter once, becomes allegedly aphrodisiac
• Attendance stat
• No presents when they're not there
• Space capsule initially filling poet's vacancy
• I left playwright during fantastic time away
• Attendance-book notation
• Lack (of something)
• Sailor wanting change of scene may take leave of it
• This shows one's not all there to sound not like the sound of 12 across