https://www.cathaypacific.com/cx/en_...alculator.html
Looks like you won't make it given that BCN to MCT via DOH gives max 25 each way on Econ (and that's if CX credits BCN-DOH, DOH-MCT).
My suggestion would be to book a status trip if you're worried about retaining CX Silver status by the end of your membership year.
Will I actually be silver until Jan 2026, or just for the few days of Dec 2024?
Unsure what you mean by this. If you have hit Silver in 2024 and don't hit the status points needed to renew by your membership year, you'll be downgraded. Cathay's system works that when you actively achieve a tier, renew or downgrade, your membership year resets on that day.