[Radek]

Your weapon will not break it it has some toughness. Here is experience of my solo characters fighting under Heroic Might + Frenzy + Haste all the time:

Toughness 20% - Suffices in Valeia. Completely unsufficient otherwise. You will have to repair your weapon after every fight in Brimloch Roon, moreover, you will have to repair your weapon during fights against such enemies like Mother of Crabs or Mystic Sphinx.
Toughness 40% - Much better but not enough. You will have to repair the weapon frequently.
Toughness 50% - Good. Well, you will need the Forge skill and you will repair the weapon but reapiring the weapon will not be your main occupation.
Toughness 60% - More than good. You will repair the weapon only rarely.
Toughness 80% - Luxury. Not needed. You can almost forget the Forge skill.

Let us note that some weapon do not have the toughness stat. These weapons try to disintgrate at every possible occasion and are completely useless (with one exception, see below). Most likely, these weapons have toughness 0% and need blessing for toughness (Artifact of Vines). An example of such weapon is the Witch's Stick. Almost unusable but if you bless it for toughness thrice (toughness 60%) and if you bless it for damage 8 times, then you get a nice weapon with damage 10 - 20 and the Sleep bonus attack. Such Witch's Stick is more than enough for Valeia and Ishad N'Ha.
There is one exception from this rule - the Assassin's Dagger. It has no toughness stat but it seems to be unbreakable! I've never seen a damaged Assassin's Dagger! What's the toughness of the dagger I don't know. In order to avoid surprises, I bless the dagger to toughness 40%.