National economic, security, and geopolitical interests of today trumps any transgressions committed in the past. Furthermore, retaking land for the sake of retaking land without considering the costs and benefits of doing so would be foolish.
That said, if at some point the situation changes in the future where 1) it is no longer in China's interests to maintain a partnership with Russia 2) there is some real strategic or economic value in the land to be taken and 3) the risks of doing so can be effectively mitigated, then there is no reason not to pursue irredentist policies towards Russia. However, there are certain factors that make it unlikely for all three preconditions to be met. The amount of land involved is not particularly large (consisting of a small wedge next to Xinjiang and a swathe in Outer Manchuria), nor is it particularly rich in rare/critical resources. The only strategic value in taking this land would be Vladivostok (which admittedly does have significant strategic and economic value). More importantly, Russia's massive strategic arsenal presents an enormous risk which cannot be mitigated or managed in the foreseeable future. Russia would need to either collapse or descend into civil war before such an operation would be feasible.
It may be more practical to just accept the lands as lost, while never forgetting the lessons learnt from China's painful history. Future generations must never forget the consequences of backwardness and weakness. All Chinese should be be aware of the past crimes that Russia, Japan, the UK, and France committed against China. The fact that Russia is China's strategic partner today does not mean that Russia's past misdeeds should be whitewashed or viewed any differently than Japan's and the UK's.
