Can you kill Sona or Renata after they use their abilities to prevent the abilities from resolving?

Ruling: No, you cannot prevent their abilities from resolving by killing them after activation. Once Sona's triggered ability or Renata's activated abilities are on the chain/stack, removing the unit from the battlefield does not stop them from resolving.

Sequence:

• For Sona: Her "if I'm at a battlefield" condition is checked when the trigger occurs at end of turn
• Once the trigger is on the stack, killing Sona does not prevent the runes from readying
• For Renata: She must be at a battlefield to activate her abilities (pay costs and put effects on the chain)
• Once her activated ability is on the chain, killing or moving her does not prevent it from resolving

Nuances:

• "Using" an ability means playing/activating it (paying costs and putting effects on the chain), not the resolution
• Renata's "Use my abilities only while I'm at a battlefield" is a restriction on activation, not a continuous requirement during resolution
• The only way to stop these abilities would be with a counter effect, though ability counters are rare
• Some effects can make abilities resolve but do nothing, which is different from countering them