1 - Generally the satellite is left behind and the tenant only returns their austar/foxtel box which is connected to the TV, the wall point and satellite remain untouched and can be used if future tenants want to have austar/foxtel connected.
2 - the satellite isn't their property so it would be very, very odd for a tenant to want to take the sattelite with them. If they want to have austar/foxtel at the new property they just contact them and arrange a connection date at the new house and again, they come out, install the satellite and do any works required.
Just to cover yourself put together an agreement that the tenant signs that they are allowed to install austar providing that the satellite remains when the tenant vacates and that any damage done to the property during installation (including but not limited to roof tiles, gutters, walls etc) or as a result of the equipment being installed that the tenant is liable to arrange these repairs be it under warranty or through an independent contractor approved by the landlord or his agent (an approved trade ensures that the tenant will not be using their cousins, husbands, friends, neighbour).
You shouldn't have any issues but better safe than sorry.