A few months old now (July), but decent enough in it's way, if no real certainty or conclusion...
This was better (April)...
Good sources with clickable links within the Le Monde Diplo article.
Thinking About the Unthinkable in Ukraine
What happens if Putin goes nuclear?
www.foreignaffairs.com
This was better (April)...
A third nuclear age may be dawning in Ukraine
Open access // by Olivier Zajec (Le Monde diplomatique - English edition, April 2022)
mondediplo.com
Good sources with clickable links within the Le Monde Diplo article.