Icons in ICON format can be generally exported to many different bitmap formats - including the TIFF. You might want to check also ICO and TIF file types for conversion, because it's exactly the same file types, just with different file extension.
Convert Icon image file to Aldus Tagged Image File Format (TIFF) bitmap image.
We found 3 software records in the database related to .icon to .tiff file format conversion.
Microsoft Windows software - convert icon to tiff on Windows
A free graphics and photo editor and authoring tool
Convert from icon file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned icon to tiff. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
A complete icon making and editing solution
A tool used to create icons, cursors and icon libraries for Windows