Some details for the Purge
Six ministers are lost in the purge.
Stalinist Head of Military Intelligence Berzin offered +5% research, but there are four other leaders with this skill.
Three other ministers aren’t particularly important.
Two Chief of Air Force leaders are lost. Smushkevich benefits TAC & CAS construction & combat but there are other ministers of this type. Alksnis provides FGT & INT construction & combat benefits and a replacement doesn’t become available until 1942. So air superiority for the SOV player becomes much more difficult.
Two or three of the minister changes are undesirable, and need to be changed out (only 1% dissent hit for each one).
Two tech teams are lost in the purge. Tukhachevsky, skill level 5, specialises in combined arms, training and large unit tactics. Vasilevsky, skill level 7, becomes available for land doctrine research in 1940 so Tukhachevsky’s loss is not important.
Alksnis, skill level 6, specialises in piloting, aircraft testing and fighter tactics, so is very important for researching FGT & INT air superiority doctrines. SOV only has one other team with aircraft testing and fighter tactics, so the SOV player may fall behind in research of these doctrines.
A total of 207 leaders are lost in the purge. 60 leaders are predetermined, the remaining 147 are randomly selected. AoD’s Stalin not only purges existing leaders, he purges some future leaders too. So it is impossible to know exactly how many leaders will remain available immediately after the purge. Of the 60 fixed leaders, 53 are skill level 1, only 1 leader has skill level 3, the remaining are skill level 2. They have a range of traits. There is a 22% chance of losing any one leader to the random selection. Here is a graph of the expected total number of leaders (army, navy, air) that the SOV player will have available if the purge is accepted or declined. It doesn’t include leaders lost in events or combat. The "End Year" data field in the leaders file does nothing in the game, unlike the "Start Year" data field. This meant that the original graph I loaded was wrong, so here is the replacement. "End Year" must have been one of those game features that someone thought was a good idea but it was never implemented.
However, as Tomnoddy has shown, there is a third choice which is to remove Stalin as Head of Govt, then the purge event will not fire.