Magic circuits cant exactly expire, for the most part they're handed down to the next generation so they can continue research on whatever the family works on.

Then there's those people whove tried to cheate the system and either butchered or done something else to their circuits in the process.

What can happen is that you overwork your magic circuits, or smth similar, in which case you're basically burning your system and nerve system and body, which is why Emiya Alter looks like a Brownie.

You'll have ro elaborate on your last question if you want an answer

If the second question you mean how a pseudo servant vessel gets chosen, the body of a pseudo servant needs to have similar qualities to the heroic spirit itself

But if you mean how they take the body of heir vessels... Idk