Virtually any escalation between Russia and the West is going to be disadvantageous to Russia.
I'm seriously surprised that the Russian government is doing this (not to mention the earlier likely attempted hits on that Bulgarian arms dealer, Emilian Gebrev).
First, if you're dealing in arms, the fact that you might be in proximity to conflict is not new. You can't just back off whenever threatened. That comes with the job. So it's probably not going to deter the arms company.
Second, if someone is exporting arms, it's probably (and in this case, definitely) a matter of national policy. That is, the government is driving the policy, not the CEO. So you're probably not killing the people who have it in for you.
Third, if you're a member of the Russian government, you are very likely reasonably personally safe. We can't (easily) stop Russian assassins (though it looks like we did in this case). But the same is also true in reverse. Russia's border is an imaginary line on the map. Russia only has the ability to provide protection to people in its territory if other countries agree not to cross that line. One of the few ways that you can personally probably put yourself at risk is by doing hits on people in other countries, because the ability to provide protection in one's territory relies on reciprocity.
Fourth, while I don't know the specifics of this German assassination attempt, and I don't know if the same was true here, the Bulgarian one was apparently covert, the idea being that the death wouldn't be attributed to Russia. That seems strange to me. If Russia's goal is to deter, then killing someone secretly won't accomplish anything. Other people must know it was them, and be sufficiently afraid of a repeat to be deterred. Otherwise, how have you gained from your assassination? Are you going to kill the head of every arms dealer in the world over and over, trying to reroll the dice until you wind up with someone who just has some unrelated aversion to doing arms deals with Ukraine?
It just seems to me like there's a lot of potential downside and not much potential upside. But I guess the Kremlin's got their own view on the matter.