I know that you're meant to use the Hoglet for The Library now (which I suspect is a sneaky way to get players used to driving the thing in preparation for Halo Kart), but there are instances where the player might decide to leave it behind because they got a better vehicle from a D20 random spawn.

However, only the Hoglet can fit through the small tunnel areas in the map. As such, you likely will need to go on foot, leaving Johnson behind.

As such, it would be a good idea for there to be Warthog grenades near the entrances to these tunnels, as these grenades spawn Hoglets. This way, you don't end up without a Hoglet when you need one.