A PVC cap on the lateral would be a reasonable solution at this point in my opinion.

The sweep of the "T" might encourage some moisture to accumulate in the horizontal portion of the pipe; but I would think that would not be a major issue in consideration of the fact that the vent in general is already going to be moisture laden and somewhat "stinky" if you will.

What's the big deal about a bit of stagnant water in a sewer vent environment anyway?

Other's will, no doubt, disagree.