Perhaps none, since Lauda has been out of DT a few times already and the world did not end. I doubt that any one person in DT is irreplaceable. There is quite a bit of redundancy. Also keep in mind that all those scammers tagged by Lauda won't automatically start to scam the minute Lauda is out of DT, nor are Lauda's ratings disappearing - just moving to the "Untrusted" part for most users, except those with custom trust lists.
I am happy I was able to convince Lauda to change his/her feedback on my account before he/she left.
It would be very hard or close to impossible.
How to resurrect Lauda:
Maybe this would work.
"Bone of the father, unknowingly given, you will renew your son. Flesh of the servant, willingly given, you will revive your master. Blood of the enemy, forcibly taken, you will resurrect your foe."
source:
https://harrypotter.fandom.com/wiki/Return_of_Lord_Voldemort