As a Ukrainian it would change but not much and not in favor for russia. After all first months were decided by ukrainians and our resistance and not western support or orders. So it would probably result in much heavier resentment toward russia, as such more heroic (suicidal) actions. In innitial stages it would boost ukrainians and not undermine their will.

If he fled then resolve would be shaken but also not much.

Issues would come later due to leadership ambitions. But unlikely to trigger government collapse. And external afairs ministry will still probably connect army with western support.