Just to avoid confusion. Technically speaking a familiar cannot function properly when
further away than 100ft. of the caster. Unless you are a Warlock with Chain Master.

But these rules can be very inconsistent, so now some additional specifications will follow:
Just to clarify: If the familiar is outside 100ft. or on another plane of existence:

• You cannot command it.

• You cannot see through it.

• You cannot return it to the pocket dimension.

• You can only sense if it has perished.

• It judges its actions based on the last interactions with its master or upon DM discretion.

• If it normally cannot attack, it still cannot attack and always preserve its life first.

• The creature loses its ability to sense where its master is; it will have to rely on its statblock and skills rolled by the DM to return.

• Upon reaching 100ft. distance from you, the familiar will warn you. Allowing you to send it to its pocket dimension.

• If the familiar is outside its 100ft. range. You can cast the re-cast the spell again and the creature will immediately return.