There do exist programs that can convert images in MrdSID format to common TIF format. One of such is Total GIS Converter for example, but there are probably other as well.
Convert LizardTech MrSID image file format to Aldus Tagged Image File Format (TIFF) bitmap image.
We found 2 software records in the database related to .sid to .tif file format conversion.
Microsoft Windows software - convert sid to tif on Windows
A dedicated converter for SID format
Convert from sid 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 sid to tif. 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 converter that is able to transform various GIS file formats