Ukraine has already been civilly unstable. A journalist being the target of a car bombing will only make it worse, though perhaps this time it's more televised and internationally known. Most people aren't aware of what's going on in Ukraine, and it's rather sad and unfortunate. But what can you do?
Journalists face danger everyday, whether abroad or at home. The fact that this particular journalist was known for exposing corruption in Russia adds the usual outrage when a journalist is killed. Journalists provide a vital service to society by informing the electorate/populace of the actions of their leaders. This killing will cause massive outrage that will lead to unrest.
No, I don't believe that Civil unrest will re-occur in Ukraine because there is no "critical mass" of dissatisfied people to do that, especially not over the killing of a journalist. No matter how horrible the killing of Pavel Sheremet is, he is unfortunately not the first journalist to get killed there and people will forget this case soon, bombarded by the news about Donbas and Olympic games in Rio.
No, if the people remain calm and committed to a nonviolent response, then civil unrest does not need to reoccur in the Ukraine. Violence begets more violence if people allow themselves to be swept up into it. If instead they stand firm and remain committed to nonviolent solutions, then civil unrest does not have to be the end result.