Endpoint Protection

I read through the manual and I cant find that if I turn on "Delete Clients After 30 Days" if they happen to show back up on the network (Ex. a laptop) will they readd themselves to the SEP Manager or does the client have to be reinstalled? 

 Client will connect back to SEPM when brought back to network.

SMC.exe on the client will always keep checking for server in 5 min ( default hearbeat )
So when Laptop connect back to network client will connect back to sepm.

You are just telling sepm to drop client but not the client to drop sepm and it is the client who always initiates communication.

As long as its a managed SEP client the client will have the information about its reporting server i.e. the SEPM. Therefore even if it connects to the network after 30 days and as rightly said by Vikram when the client initiates the communication and the moment it finds the requisite server it will start communicating with the server

if you have synchronization with AD? And differences?