[Goose]

I agree that a Ukraine without Donbas and with a Russian land corridor cutting them off from the Sea of Azov is not a viable state. 

If Ukraine can limit Russia to the territory you described, but retain Odessa, Mykolaiv, and Kherson, why would Ukraine be non-viable?

IMHO, two reasons. Mariupol is a key port on the Sea of Azov. It exports a large percentage of Ukrainian grain and other products. It is the only port on the Sea of Azov with such large port facilities. It is also a major manufacturing center. If Russia keeps that strip of land, Ukraine can't use the M14 highway either. Odesa is just not a big enough port to supply Ukraine's needs. Historically it is the countries third choice, with Sevastopol and Mariupol ahead of it. Odesa is at the "far end" of the country. Lots of exports would have to go a long way.

The second reason is that Odesa is geographically just too easy for Russia to blockade. With the land corridor to Russia proper, Crimea can be supplied for sure. From there, Odesa is always at risk. The German navy tried to run a war out of Odesa. They gave up. Too hard to do. Ukraine can't constantly be at risk of being cut off. Nobody is going to invest with Putin sitting on such an advantage.

[Goose]

I agree that a Ukraine without Donbas and with a Russian land corridor cutting them off from the Sea of Azov is not a viable state. 

If Ukraine can limit Russia to the territory you described, but retain Odessa, Mykolaiv, and Kherson, why would Ukraine be non-viable?

IMHO, two reasons. Mariupol is a key port on the Sea of Azov. It exports a large percentage of Ukrainian grain and other products. It is the only port on the Sea of Azov with such large port facilities. It is also a major manufacturing center. If Russia keeps that strip of land, Ukraine can't use the M14 highway either. Odesa is just not a big enough port to supply Ukraine's needs. Historically it is the countries third choice, with Sevastopol and Mariupol ahead of it. Odesa is at the "far end" of the country. Lots of exports would have to go a long way.

The second reason is that Odesa is geographically just too easy for Russia to blockade. With the land corridor to Russia proper, Crimea can be supplied for sure. From there, Odesa is always at risk. The German navy tried to run a war out of Odesa. They gave up. Too hard to do. Ukraine can't constantly be at risk of being cut off. Nobody is going to invest with Putin sitting on such an advantage.