You might be better off exporting each elevation to its own layer.
Then you can introduce a snapping tolerance for the lines (like 10m)
This will be dependent on the size and length of the gaps.
You might think using
Creating lines that connect to other lines it the correct approach:
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//001t0000002r000000.htm
(but is still 98% manual work)
This method below achieves better results faster (more automated).
Then ArcGIS has a Feature to Polygon (Data Management)
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//00170000003n000000

This can preserve attributes (elevation) values.
There always might be some manual snapping and cleaning of data (time consuming).
tip: use your source data a background check and snapping source to
Then you can then convert these back to Lines
Lines to Polygons (Data Management)
http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#//00170000003t000000
Geowizards can help out too (under free tools)
http://www.ian-ko.com/