I'm more on that he got killed by Boris Goldberg. They were having a big feud before his death. There were two times when Evsei got attacked, but the style kind of reminds me of how LCN kills people. I think it was Goldberg all behind it.

And a correction from me, I before mentioned Balagula and Nayfield, the two mob bosses were Balagula and Goldberg who were scared of Ivankov.