Given the mood of the Iranian people, even if the government wanted a ceasefire I don't think they can. The time for talk is long past. Israel finally bit off something they can't chew up.
Public opinion was probably the major reason the IRGC wasn't able to properly respond to Israeli aggression until now. The Iranian people now properly understand the position of the hardliners and IRGC. The zionists chose war and it's what they are going to get.
I don't know how long this war will last but my guess is this has at least another month. This reasonably gives Iran enough time to punish Israel and deplete weapon stocks.
The union state is basically an attempt to bring together former soviet republics after the ussr collapsed as some kind of political continuation. It would be weird for Iran to join. Iran joining the CSTO would make more sense but that has been losing members because of American imperialism and Russia's foreign policy in reaction to that.