Iorveth can be nice even on Roche's path, but only if you gave his sword back, trust me.Aver said:He said: "Should I terminate them?". He asked if his orders are to terminate them. He didn't say that he is ready to do so or not. He helped Witcher in Nilfgaardian camp in ACT2 even tho Geralt kinda betrayed him earlier.
Iorveth isn't nice anymore if you choose Roche's path.
And that "Should I terminate them?" Sounded more like "I do it if you ask for it" than " I don't want to do it, only if really necessary", but it is entirely possible that this is only my opinion. Also, there are dialogue choices where the first words of welcome from Roche in Act II Iorveth's path aren't that...kind.
Oh...and in my opinion, Geralt owed nothing for Roche, only that he catches the kingslayer, which he does, so no betrayal here by siding with Iorveth.