My understanding is that you can go onto cows milk after 1 year and only really need to carry on with formula if you toddler is a fussy eater and therefore you are concerned about whether they are getting all the right nutrients in their solid food - which they would therefore get from formula.
I am amazed at the number of kids that still drink so much milk - a 15 month old only needs 400ml per day, so my 15 month old has two milk feeds - one in when she gets up and one just before bed - much less hassle than giving her milk several times a day.
OP I would not worry if you toddler does not want to drink milk in the day, but perhaps bring dinner time forward so that he/she is more hungry for milk before bed.