It's complicated. As collateral for all the energy the Master puts into the summoning, they get three unbreakable 'Command Seals'. When all those are spent, in my War at least, the Master would die. Certainly, it's not impossible for a Servant to reject their Master before those even come into play, though; I know a girl back home who became bored with and slaughtered her Master early on. It's not slavery, if that's what you mean. From a certain perspective, a Servant is a Heroic Spirit only is recorded and exists to be summoned back from the dead or dreams of the past, in a normal Holy Grail War.
I'd recommend talking. to one of the ones here and getting their stance on the matter, myself.
no subject
I'd recommend talking. to one of the ones here and getting their stance on the matter, myself.