This marks a type of turn in the war. While Russia has gained some ground in Eastern Ukraine it also is coming with increased cost. They are loosing diplomatically and economically. Military strength has somewhat been tarnished. It is not guaranteed they will continue to make headway as Ukrainians create countermeasures and receive new equipment.
While this may mark a turn in internal dissention, that appears to be growing, it does not mean that Russia is down for the count. What it does mean is that he will now feel internal pressure, in addition to external pressure, to end the war. Sustained pressure that leaves a diplomatic "out" for Russia to leave Ukraine is important.
As a make it or break in historical time for Putin, he may seek to double down on efforts which will likely have mixed results. What it will likely do is increase internal pressure to remove the president from his position. High ranking officials and oligarchs may start thinking about the long term health of the nation and devise desperate/alternative strategies with a new administration.