If I remove from service one of the real servers from the farm for maintenance, (no inservice), will it drop all connections to that real right away or will it let them gracefully close as the users close their sessions to that server?
No new connections are allowed but existing connections are serviced. From the IOS SLB config guide -
Does the no inservice command take a resource out of service immediately?
When you use the no form of the inservice command to remove a firewall, firewall farm, real server, or virtual server from service, the resource acquiesces gracefully. No new connections are assigned, and existing connections are allowed to complete.
To stop all existing connections for an entire firewall farm or virtual server immediately, use the clear ip slb connections command
