Without going into details, I managed to delete a server today. i relaized 
it immediately and had it rejoined within 30 seconds. I neglected to 
configure the managed subnets however and it was about 20 minutes later 
that i remembered to do so.

Most users were able to log back on without any problem(many even before I 
added the managed subnets).

Not many, but more than a few, were caught in some wierd twilight zone. 
Although they were not logged on, when they clicked on the agent icon they 
were presented with the logout option. Clicking on logout, the 'sucessfully 
logged out' screen would appear. Click on the icon again, and the logout 
option appeared again. Click on logout and the 'successfully logged out' 
screen appears. Click on icon again and the login option finally appears. 
Click on login and...'sucessfully logged out' screen appears.

If a computer exhibiting this behavior is on the same subnet as the server, 
this does not happen.

If you log on through the web interface from an affected computer with a 
role that does not require the agent, access the manager and delete the 
user session, problem solved.

Conclusion: It is a bad isea to delete servers.