Once the Beast token has attacked or blocked, removing all of your other attacking or blocking creatures won't cause it to stop attacking or blocking.

If you control more than one creature with "This creature can't attack or block alone" they can attack or block together, even if no other creatures attack or block.

If an effect says the Beast token attacks or blocks "if able" and you control one or more other creatures that are able to attack or block, you must attack or block with the Beast token and at least one other creature.

Although the Beast token can't attack alone, other attacking creatures don't have to attack the same player, planeswalker, or battle. For example, the Beast token could attack an opponent and another creature could attack a planeswalker. Similarly, other blocking creatures don't have to block the same creature that the Beast token blocks.

In a Two-Headed Giant game, the Beast token can attack or block with a creature controlled by your teammate, even if no other creatures you control are attacking or blocking.