It ends when Pupin’ quits abusing his neighbor state’s sovereignty.
End of story.
I’d be very careful of a summit. Any compromise, will be a compromise regarding Ukrainian sovereignty.
That should not even be on the table.
Imagine the Ukraine sending mercs into Russia, then trying to set up a summit to compromise. No, Russia would demand it simply retreat and stop all hostilities.
Russia should work from that model, without a summit.
And don’t forget (I know you haven’t) that Russia has already gobbled-up a piece of Ukraine.