You can buy an electric generator from Germany, US,... is not that easy, it takes a while to manufacture and it is not a perfect solution at all. You can import electricity and perhaps improve the infrastructure to import which is no off the shelve, but is not high tec either. The attacks on Ukraine power grid are to be taken seriously, but they will not stop the Ukrainian army.
They will not stop the Ukrainian army, but they will stop the Ukrainian military industry. The main goal of attacks on the energy system is to make Ukraine completely dependent on arms supplies from the West and not be able to do anything on its own.