The East (and Dniepropetrovsk) is the main Ukrainian industrial centre. If Ukraine lost the East it'd be an agricultural country. However, the both "people's republics" hold just a part of it. Kharkiv, Dniepropetrovsk are in the Kyiv's control.
It's interesting that some Ukraininan insdustry has provided Russia with military tech (like aviation engines, planes) and serviced Russian liquid-fuel nukes (Satans). Now the Ukrainians are likely to loose this market. And many workers may emigrate to Russia over all this.