Of course there is a down side to letting a player of a recently deceased character take over an established NPC. It can be like a complete personality transplant. If you're lucky.
If you're unlucky, it's a complete character backstory and campaign history transplant.
GM: Okay Jim, you're Padmé now.
Padmé: Right. What have I been doing while Qui-Gon was heroically saving the day?
GM: You got captured by some droids in the palace.
Padmé: I lay down covering fire and dive out the window with my guards!
GM: Um. This has already happened. The droids took you to—
Padmé: I use my Rogue skills and fire ropes to climb up to the throne room level!
GM: Er... Okay then. The droids surround you there and keep you prisoner until—
Padmé: The decoy Queen creates a diversion and I take charge using the blasters I have concealed in the throne!
GM: <sigh> Fine. You capture the Trade Federation leaders in the throne room. Their headquarters is destroyed and the droid army deactivated anyway. So it makes no real difference.
Padmé: Cool! I get experience for this, right?