How much worse can it get... well, hypothetically speaking, imagine a scenario where: power in Russia collapses - a fight for power ensues - possible independence movements - and parts of Russia become a "no man's land", free for the sacking. Who knows where are all the nuclear warheads in that massive country, and if a post-collapse Russia, and whatever entities that remain, would have the capability to ensure the safety of those warheads or if they would even allow UN to get in to atleast secure those warheads and nuclear powerplants.
Can you imagine a scenario where even a handfull of warheads become available in the black market? Not to mention the scenarios where someone even worse than Putin reaches power, cleans up the remainder of people that still had some common sense to avoid the usage of nukes, or Russia spliting into several countries, all of them with some crazy leader possibily with access to some nukes as well.
Right now, all we can do is wait and see, but there's no guarantee that someone decent climbs to power and Russia becomes a friendly country and just leaves Ukraine.
It can be great, it can be terrible, depending on the outcome of whatever happens in Moscow.
