After a breast lift with implants surgery, if I were to lose weight would that cause my boobs to sag again ?

How much your breasts would change depends upon how much weight you lose. If you lose a little weight, you may notice minimal change. If you lose 100 pounds, there will be change. I suggest you lose the weight you want before the lift.

Dear applesaresoymmy22,
any major changes in weight will also cause changes in breast shape and size. So, if you lose much weight your breasts will probably deflate and sag.
Daniel Barrett, MDCertified, American Board of Plastic SurgeryMember, American Society of Plastic SurgeryMember, American Society of Aesthetic Plastic Surgery

If you were to lose weight would your breasts sag again? The true answer is maybe. Weight loss of five to ten pounds won't likely have much of an impact on your results. However if you lose 50 pounds then you may see changes. Other factors that can influence your results are pregnancy as well as the size of your implants (larger implants are heavier).