The VisibleRange property can hold the actual visible minimum and maximum of the axis while the chart is being zoomed and panned.

Let's say I set the number of labels to 4 on that axis (see attached pic).  It would then be up to the axis to auto generate the labels depending on the data and zoom.  There would always be four labels shown on the axis regardless of zoom so the user could always have context regardless of the zoom.  The labels would just change to reflect what is currently being viewed at the current zoom level.