With ds I worked three 12 hour days a week from 9 months onwards. I initially expressed twice a day and nursery gave him 1-3oz ebm in a cup morning and afternoon. At 10 months I dropped this to morning only, and by 12 months I stopped expressing and he had food and water when away from me. When I was around he breastfed on demand (maybe 6 times per 24hrs?).
He had cows milk products as part of a varied diet, but drank no cow's milk. It never caused any issue tbh.
The only recommendation in relation to milk after the age of 12 months is in relation to ensuring toddlers have sufficient calcium intake. However, the requirement is actually fairly low. The Food Standards Agency say that children between the ages of one and three need to consume an average of 350mg of calcium a day. If it was just coming from whole cow's milk then about 3/5 pint a day is needed. But yogurt, cheese etc count too, as well as non-dairy sources like sesame and of course breast milk . This has a list of calcium contents:
www.nnuh.nhs.uk/docs%5Cleaflets%5C197.pdf
Calcium from human milk is absorbed over twice as well as calcium from cow's milk, so is like drinking double the amount .
Like others have said, toddlers can be more flexible about breastfeeding. some people continue to feed on cue, others set rules and limits or gradually cut them down. The World Health Organisation recommends that all children should be breastfed until the age of at least 2 years because of the significant immunological and nutritional benefits.
I used to stay out for works things occasionally and miss bedtime sometimes from about 15 months. The first point was that I had to express or I would have burst, lol. Ds was fine with dh, who just cuddled him to sleep. I would then pick him up and feed him when I got in.