Only Wajib and Masnoon I’tikaf are rendered invalid. Nafl I’tikaf is not rendered void by any act. It is merely ended by engaging in an act which is not permitted for the Mu’takif.
Unnecessarily leaving the Musjid for even a minute whether intentionally, unintentionally or under compulsion, will invalidate the I’tikaf. All acts and reasons besides the valid reasons (see page 35,36) will be regarded as ‘unnecessary’ in the context of I’tikaf. Thus, leaving the Musjid due to illness, although permissible, will invalidate the I’tikaf. To leave the Musjid for Jannazah Salat, visiting the sick or for an other permissible activity besides the VALID REASONS (see page 36,37), will render the I’tikaf null and void.
The Itika-f will also become void (break – be invalid) if the Mu’takifs fast breaks.