The diagram control does not impose any limit on zoom factor, but it seems browsers have a limit on the size of the Canvas element. In my tests with different browsers, Firefox reaches the limit first at about 10000 x 10000 pixels, so after zooming in you might check the canvas' width and height values, and restore the previous zoom factor if width or height got larger than 10000. I can't reproduce JavaScript errors, but you could try / catch for ones and restore zoom factor from the catch block too.

If you need to enable larger zoom levels, you could set smaller diagram.Bounds value before calling setZoomFactor. E.g. make Bounds size inversely proportional to the zoom factor and it should allow zooming into some area of the canvas indefinitely.

I hope that helps,
Stoyan