As you said, you need to use sorbate unless you can sterile filter, the Lysozyme really has no lasting effect in the wine, it completes the job of killing lactic bacteria over the period of several days, after that, the enzyme activity diminishes over time depending on tannin levels as well as fining treatments, in fact, bentonite will quickly deactivate any remaining Lysozyme. The wine should be ok if SO2 levels are appropriately maintained from now through the bottling process, just add sorbate if sweetening.