The boots of lead spell doesn't state that the lemure would be consumed with the activation of its effects (although the rulebook says that usually they dissipate/explode/are consumed when the effects are activated).
Then again, her other spells have a "as long as the lemure is in play", which doesn't indicate that the lemure would be consumed by its magic while the effects are active.
I also looked at Sara's spells and even the exploding lemure is not marked as consumed by the effect.
So more or less, when lemures are NOT consumed by their effects?
My understanding is that the lemure is destroyed whenever the spell effects are triggered unless the spell they carry specifies that they remain in play (the "as long as the lemure is in play" you mention).