If Sophia is killed, there is no way anyone would stop Ellsworth from finding and killing Hearst, where ever he might go, short of killing him(Ellsworth), too.
Makes sense. Or he just wanted to control his own fate. If he came at Steve with a shotgun, no guarantees Bullock does not stop him, or force him to shoot him, too.
I, while surprised, was not shocked by Hostetler suiciding. In an earlier episode, (last season, I think) he made a comment along the lines of: "Before they can hang me, I'll blow my own head off." My interpretation is that he realized that he would never be "permitted" (by Steve, mainly) to...