Cookie consent solutions' impact: how many GA users are we losing?

I read some about GDPR and GA.

I understand that, without cookies consent given by users, we loose most of the deepest user behaviours.

But I haven't seen what happens to my users traffic in details.

I mean, if I have 25% of users refusing cookie consent for GA, will I loose 25% of users in the basic traffic measurements, i.e. visits, sessions? Or will I loose only some more advanced metrics, i.e. returning users, e-commerce sales, time to conversion and so on?

The comprehension of this argument is important to understand how many users I lost from the year before when the cookie solution wasn't applied on my properties.

Thanks to all