This is a fairly rare, but known issue. The game kills off all Leandra's summons once she is dead, but somehow the alignment for 3 of your characters was changed so they are also effected. This will be fixed in the next update, which is currently being tested (no official ETA yet, but if there are no serious issues found, nothing else gets added and there are no organizational or other delays with the release itself, hopefully it will be out in a couple weeks, or so).
