A defect on the front element coating is usually less serious than damage near the rear element or dust on the film/sensor plane. Based on the answers here, it may have little to no visible effect in many images.

If it does show up, the most likely issue would be some kind of faint spot or localized reduction in contrast rather than a dramatic optical failure. In practice, many photographers would simply shoot with it and check the results.

To minimize any chance of visible problems, be most cautious with scenes that include strong light sources or bright glare hitting the front of the lens, since front-element issues tend to be most noticeable there. For general landscapes, portraits, and close subjects, you may see no meaningful effect at all.

If a small spot does appear, it will often be easy to correct in post-processing with healing or cloning tools. So the practical advice is: use the lens, avoid harsh direct light into the lens when possible, and rely on your cleaner 180mm lens when you want extra peace of mind.