I had a very cautious opinion Charlie Kirk. My impression of him being such a prominent figure on the right was the equivalent of the high school quarterback who just so happened to be the son of the team's coach. That is, I am not entirely sure that he got such prominence based solely on his merits. And it might be the case that the son of the coach shows some competency and plays well as the quarterback. And I could say the same about Charlie Kirk, as he has remained influential on the right.
The reactions of many on the left in various social media platforms is no surprise either. There were plenty of gleeful posts that are glad he is dead, though it comes off as far more spiteful since he was murdered at a very young age rather than someone who died old and with health problems, such as Rush Limbaugh.
Charlie Kirk was by no means extreme in his viewpoints, regardless of what is said about him from those on the left. For many of them, anyone moderately right wing is considered a hard core right wing extremist. So I do not think that they will be convinced that Charlie Kirk being killed will bring about an even further right wing figure. Because they are all Evil Fascist Nazi's in their eyes.
I know there were voices on the left that spoke out against him being killed and condemned anyone taking joy in his death, though we cannot know for sure whether or not this is geniune or simply performative. From a public eye standpoint, it makes sense to condemn violent extremism regardless of your personal feelings. And in a way, even if you are just putting on a performance, it does show you to be truly different from those who publicly celebrate his death.