My daughter also drinks much lesser milk since few weeks ago. I think it's ok. They all are over 1-year-old, approaching to be a toddler, not a baby. They need more nutrition from solid foods instead of formula.
My baby already refused to drink formula milk many months ago.
But we still give him formula milk with rice cereals twice a day. The nurse at the government clinic said baby still need to have 2 bottles of milk everyday. So even if baby refused to drink milk, still try to make them drink (or with cereal in my case).