You can use it as long as you want because the odds of you getting an upgrade to begin with are really low. Loot is hard to come by in Classic compared to modern WoW.
My guild in classic went all the way to Naxx and I never got a two hander better than Untamed Blade from Blackwing Lair, or finished my tier 2 wrath set. Meanwhile our druids and warlocks were completely pimped to the point that many of our guild were rolling alts in those classes to pick up loot rather than have it just be disenchanted. You are simply at the mercy of RNJesus.