A new variable, the autoclean_novehicles was introduced in the version 0.7.0, which specifies the amount of months after which an inactive company without vehicles is removed, regardless of the password setting. This is to prevent players from creating 'empty' companies.(autoclean_companies) will have to enabled for this option to work.)
Max value - 256 months ~ 21 game years
Please note that when settings this value to 0, it disables this option.