Bukovina, just IMO (and reinforced by the recording of Hitler-Mannerheim), accelerated the invasion of the USSR since it pointed out the German dependance on foreign oil.
the Winter War comment was in reply to your questioning whether it would even take place, which i think it would, but possibly the occupation of the Baltics would seem an easier task first?
I think the Baltics will be invaded by the Soviets (after all, it was negotiated by Molotov). Bessarabia and Bukovina, again, seemed to be moves typical of Stalin so I'm not sure the alternate Collegial Dictatorship would go that way. Let's study the men: Voroshilov is an ultimate imbecile unable to take any initiative; Mikoyan is, by definition, an effective administrator and extremely cautious man; Kaganovich never dealt with foreign politics and Molotov did because Stalin put him there (even if it became a source of pride and satisfaction for him: again, see his rivalry with Litvinov). Stalin remained the main (if not sole) architect of Soviet foreign policy in 1939/1941: Molotov followed but didn't create.
So most plausible outcome: Molotov and cie stick originally with the MR pact, secure the Baltics and probably their piece of Poland.
Winter War is not an absolute certainty but may happen since Molotov always agreed with Stalin that Leningrad needed to be "secured". Negociations will surely occur but without Stalin, Molotov may be less coarse and agressive with the Finns. Mikoyan may in fact moderate him. Again,
Drakonfin seems the best source of information on this forum.
Romania? Can happen but less certain than the Winter War.
Katyn is practically avoided. Officers will be sent to gulags and likely kept as some sort of bargaining chip (Stalin's circle was for this idea initially).
Kulik, one of Stalin's favourites and the scourge of Soviet modern artillery and tanks, will considerably lose influence, even without the Winter War. Kaganovich didn't like "experts" and "technocrats" (about industry) but Molotov and Mikoyan were pragmatic in that regard: if everyone insists that T 34 needs a better gun than the one proposed by Kulik, they'll pay attention for example.
NB: About Romania. If the Soviets don't move and if the Germans grant the Hungarians their 2nd Vienna Award, Romania, while still anti-communist, will be immensely pissed off. They may be pressured by Germany to sell them oil and wheat but they will then become the Sweden of the Balkans, until they see an opportunity to stab Hungary in the back.
I'll add that my knowledge about the period and mentioned locations is limited to Khlevniuk and Montefiore's books, plus this forum. So it's likely far less extensive than others'.