No you will not loose your GPS data. It will get rid of any setting you or anyone else made to prevent having SI and DI.
Use SIMULATOR, that plays a recording that the unit processes just like when in Normal use. If you don't get SI and DI views after doing a Restore Defauts, your unit is faulty.
Humminbird Helix 12 CHIRP SI, 1198c SI, 1198c SI, ONIX 10 SI NT, Helix 7 CHIRP SI GPS G2, SOLIX 12 SI, 360, RC-1