Buying VOD would present VZ with far more financial, regulatory and political hurdles and costs than simply buying the minority stake in VZW. Since all VZ wants is VZW, it makes sense for them to keep it simple.
Also, VOD wants to remain independent and wants to exit its minority stakes, and it also wants more cash with which to make acqusitions. So it seems that both VZ and VOD want a VZW deal at the right price for them, whereas neither wants to merge or be acquired whole.
EIther way, I think VOD is in good shape. A stalemate is fine for VOD since they'll contine to get nice VZW dividends and won't be able to blow a wad of cash on big EU acquisitions. If VOD sells its stake in VZW, then VZ will have to pay up.