I don’t remember the bridge in II, but in the first one I remember having to go back to an earlier save after I wasted an item and then kept playing for a while.
It’s true that in games like Avernum you can make the game unwinnable if you don’t have proper backup saves and then save in a bad situation, but always keeping a saved game in a town will prevent that from happening. You can’t make it unwinnable by wasting items.

In the original Exile you could probably ruin your game by building your characters badly enough. Only the first one had danger of that happening, and even there it was unlikely that you wouldn’t realize it in time. You need graymold salve at one point. In Avernum you have someone make it for you. In Exile there was an alchemy skill that let you make potions. You could buy potions, and it wasn’t really worth it to build up alchemy, except that it was the only way to get graymold salve.