Odessa will be the next flashpoint.
If Putin intends to carve off more of south eastern Ukraine, to conitnue what he is announcing as his “protection,” of the ethinic Russians in south eastern Ukraine, then he may well move on Odessa next.
However, I think it may also be likely, that he will seek to get the provinces further to the east too order to establish a land corridor to the Crimea from the Russian border. That would mean any or all of the following would also be at risk. Luhans’k, Donets’k, Zapurizhzhya, and Kherson.
Just depends at this stage on what Putin thinks he can get away with wothout major consequences.