AD Integration... deleted system accounts?

Hello

I have a user that, I believe, deleted some AD/Exchange SYSTEM accounts from the users panel. My fault. But has anyone ever done this? Everything seems to be working fine and I haven’t seen any error messages yet. I know this is a bad no no and I’m expecting to rebuild everything at some point in the not too distant future probably, just curious if others have done this/seen this? Ideas… thanks.