On the other hand once Slovyansk and Kramatorsk are taken Putin might decide to keep going, because there are dramatically less defensive structure beyond those two cities.
Slovyansk-Kramatorsk-Konstantinovka are the three main fortress cities of Donbass built up since 2014. Konstantinovka is already 90% gone and Russians are about 7km from Slovyansk and Kramatorsk. Once they are all taken it's just flat ground beyond them. Compare current situation to 1943:
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Red Army took the three cities around 6th of September and broke the German line there. Then they chased Manstein's forces all the way to the Dnieper River before the offensive was over, advancing 300km by 22nd of September.
It's not beyond imagination that if these three doorway cities all fall a similar route could happen again, if on a smaller scale.