Union contracts don’t just expire. The contract has a 3 year term. At that point, an updated contract will need to be negotiated. If the 3 year period ends without a new contract, but the new parties are still making progress in the negotiations, the workers will continue to work under the terms of the old contract until the new one is completed.
If the negotiations are not going well, if they reach an impasse, then strikes or lockouts can happen.
Regardless, any terms in a union contract cannot be removed unless both parties agree to their removal. AI advancement or decisions by the studios could very well lead to another strike in 3 years, but any terms related to AI, or any other language in the contract will not automatically disappear at the end of the 3 year term.