Will my hand be cut off and will expiations be due from me for taking a sum of money from the treasury without anyone's knowledge, then returning it after about a year?

What you did, betraying the trust, is forbidden, due to the words of Allah the Almighty: "O you who have believed, do not betray Allah and the Messenger or betray your trusts while you know [the consequence]," and due to the words of the Prophet, peace and blessings be upon him: "The signs of a hypocrite are three... and if he is entrusted, he betrays."

Therefore, seek Allah's forgiveness for what you did, regret it, and resolve not to return to it. Conceal yourself with Allah's concealment upon you. Your obligation has been fulfilled by returning the money and restoring it to its rightful place. And Allah knows best.