Entrepreneurs will do whatever it takes to make money and sugar coat the story. The reality is that even if no slaughtering may not be involved, please consider the following:
- Cows must still be (unwillingly) impregnated, so they can get pregnant and produce milk
- Cow's milk will be stolen from the baby calf so it can be sold to humans
- Cows milk production drastically drops after they age and go through few cycles (which is why slaughter is common practice)
- Even if slaughtering isn't directly happening on the farm you're purchasing this milk from, they may have other mechanisms (that are for example used in India), where the farm is selling the cow to another company/entity that slaughters them later on anyway (for meat or leather).
In my opinion, if the intention is to eliminate or reduce the suffering of cows, then slaughtering isn't the worst thing they experience (in my opinion). I think that the suffering comes mostly from sadness for their children that were taken away and being raped/imprisoned for their entire life. They are constantly in this 'cycle' without any choice whatsoever, they can't even kill themselves if they wanted to.
While I think there might be some extraordinary scenario where we could use the extra milk that cow doesn't need and they live in a total freedom and good life, the milk price in this scenario would be very large, like 1000 USD per litre. There's also no good reason why we would need such a substance as nowadays cow's milk is obsolete for humans.