In "I will repay" Richard Lambert disintegrates to dust after Nick staked him. He was just a few days old.
Spark (A More permanent hell) and Vachon both drop dead, but their bodies appear to remain intact. They were older than Richard of course. What is the minimum age that is required for the body to remain intact?
And then there are those who do not stay dead at all inspite of being staked because they are much too old and powerful (Lacroix). But also Alexandra (Fatal Mistake) who is staked by Nick in the car wrecker's lot and re-appears afterwards, and Francesca whose soul survives (we don't really know what Nick did with the body to prevent her from coming back intact).
What is the minimum age for a vampire to survive a stake? Is Nick already old enough to survive the end of "Last Knight" (in case Lacroix really does stake him)? Alexandra is several centuries younger than Nick, and she came back. Or is it something in Lacroix's blood that his children have inherited, which enables them to come back? In that case, Nick would also be immune to a stake.
Any thoughts or theories to share on the matter?