When playing as Sett, can you generate 1 energy before recycling 1 rune as a reaction to his replacement effect?

Ruling: You cannot directly react to a replacement effect, but you will virtually always have a chance to exhaust a rune and float energy before anything happens that kills one of your units. You can react to the spell or ability that's going to kill your unit, or exhaust a rune in combat before combat damage is dealt.

Nuances:

• The rules can be updated to be broader and include replacement effects, which would let you pay for abilities like Nocturne or Sett and float energy while doing so
• If you float power for Sett's ability, your opponent could still react to prevent the unit from dying, leaving you with floated power you can't use