The question seems to assume that a security council resolution is necessary to try somebody for war crimes. This is incorrect.
The ICC is at liberty to investigate crimes within its jurisdiction, which is described in article 12 of the Rome Statute as follows:
- A State which becomes a Party to this Statute thereby accepts the jurisdiction of the Court with respect to
the crimes referred to in article 5.
- In the case of article 13, paragraph (a) or (c), the Court may exercise its jurisdiction if one or more of the following States are Parties to this Statute or have accepted the jurisdiction of the Court in accordance with
(a) The State on the territory of which the conduct in question occurred or, if the crime was committed
on board a vessel or aircraft, the State of registration of that vessel or aircraft;
(b) The State of which the person accused of the crime is a national.
- If the acceptance of a State which is not a Party to this Statute is required under paragraph 2, that State
may, by declaration lodged with the Registrar, accept the exercise of jurisdiction by the Court with respect
to the crime in question.
Since Ukraine has accepted the jurisdiction of the ICC for all war crimes that occurred in its territory, this condition is met, and the ICC has, in fact, opened an investigation.
As for precedent:
During the NATO bombing of Yugoslavia in 1999, Slobodan Milošević was charged by the International Criminal Tribunal for the former Yugoslavia (ICTY) with war crimes in connection with the Bosnian War, the Croatian War of Independence, and the Kosovo War. He became the first sitting head of state to be charged with war crimes.
Of course, arresting a head of state met with practical difficulties. However, after he fell from power in 2000, he was apprehended by local authorities, and, after significant international pressure, extradited and stood trial. He died in 2006 before a verdict was reached.
You are correct that no head of state of a permanent security council member has ever been tried for war crimes, but that may simply be because none have ever been accused of such. Since the security council plays no role in such proceedings, and apprehending the suspect practically requires cooperation of local authorities even if that nation doesn't have veto power in the security council, I don't see why the veto power would matter.