Seriously? That doesn't really make sense to me. If you get the note, off his dead body alive or dead, Zaleskar should still respond to Ifan. Ifan would probably kill magister Borris anyway because that just seems like something Ifan would do.
However, however Ifan has to be the one to speak to magister Borris or in the party to loot the note. So, then yes it makes sense that Zaleskar doesn't respond to Ifan.
Ifan (Silver Claw) is like in a gang (lone wolves), if part of their mission is interrupted, there is a signal sent to abort. There is always someone working in the background to let the next part of the mission know if it's been interrupted.
Honestly, if you don't have Ifan and do his quest line where he gets the note, then Zaleskar shouldn't even be there.