As it happens sovereignty is a binary thing, at least when looked at domain by domain. Either you are sovereign or you are not, there is no half-sovereign.

The EU is going the federalisation way. Even now member countries relinquished sovereignty on key aspects: border control and immigration, monetary policy and currency, trade policy, and then a bunch of other things. This is hugely significant for a country.

This is just a referendum on talks so won't "seal their fate" but kudos to them for holding it.