An assassination might not "change the dynamic" in an appreciably better way.
One could not be sure of anything going forward after Putin had initiated the invasion of Ukraine. Even the best of military advisers acknowledge that with the first shot fired, what happens and what was planned begin to diverge.
We don't really know what level of support Putin truly had then or truly retains now. If someone were to assassinate Putin, no one could foretell what would then ensue, either with respect to conclusion of Russia's aggression in Ukraine, or regarding political / military / social upheaval in Russia. In any case there would remain the grotesque economic burdens Putin has brought down upon his country by persisting in a military operation that only five countries in the world don't condemn him for. He is able to continue this assault upon Ukraine only because everyone fears escalation to use of nuclear weapons.
The destruction of life and infrastructure in the Russia-Ukraine conflict is horrendous. There is no guarantee that it would cease upon the assassination of Putin. No assurance of effective regime change either. No assurance that whoever seized power would not threaten to use nuclear weapons in Ukraine. Doubtless one result would be a fast spreading conspiracy theory that Ukrainians somehow managed the assassination. It would serve every Kremlin insider working meanwhile to gain enough power to take over.
There is no succession plan right now except that the prime minister steps in as acting president for a maximum of three months, after which elections shall be held. Who gets to stand is determined behind the scenes by elites and the upper house of the parliament. Prime Minister Mikhail Mishustin is a technocrat, an economist, a tax guy and a supremely bland politician, which is the only reason there even is someone in that slot, else Putin would have done away with it in one of his unending assaults on the efficacy of Russian government checks and balances over the years. It's not clear he'd become the favorite, and it's not clear who would have enabled that behind the scenes either.
Foreign Affairs ran a piece earlier this year about potential power struggles when Putin ceases to lead Russia (for whatever reason).
Russia’s inevitable succession crisis
www.foreignaffairs.com
So how can one think an assassination of Vladimir Putin would serve anyone's interests? It will not bring back the dead. It offers no guarantee of stopping the dreadful slaughter and mistreatment of civilians in Ukraine. And... the very question of who would do such a thing certainly circulates amongst those inside Russia who already wish Putin were no longer head of state, but the fact that no one has done it during the extension of this debacle suggests that the man is not without effective support even now. All that killing Putin would do would be to insert a new level of apprehension about how the conflict in Ukraine will finally come to an end.