one thing j remember from Fate Zero is that you can kill your master and have someone else take over the bond. Though maybe that was an unusual circumstance since the guy who took it over was a judge or whatever.
That is indeed a thing you can do. The catch is that Servants can't exist for very long without a Master present to provide them mana (or prana I always get tripped up on these) and will die/disappear if they don't form a new contract quickly. I forget the general timeframe they can exist like this, but I'm pretty sure it's under 24 hours... though if they possess the trait Independent Action they can make it a lot longer, like a week or something.
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xp1337: Don't you wish there was a spell-checker that told you when you a word out?