Lips Still Slightly Swollen 10 Months After Lip Reduction, How Long Until Completely Healed?

Since it has been over 10 months, your lips may be close to the size they will be.  You might wait until a year, and then if too big, consider a repeat reduction.  It is better to err on the full side with a lip reduction.

Operations done on the full length of the lip such as VY advancement of the lip lining forward to increase the amount of "pink show" or lip reduction to reduce lip bulk interfere with the lymphatic drainage of lips and often result in prolonged swelling that may lat a year or more. By 12 months you may be looking at the end result and need to accept it or discuss your options with your Plastic surgeon. 

The strong liklihood is that after 10 months what you see is what you've got and that the healing is essentiallu complete.  Give it a full year but if they are still too big, a second reduction might be in order.