After the 2.37 update, Rocket Buggy, along with the PK IFV, S-13 (which was added back later), Humvee IFV, and Stryker are removed from the game. Players who had access to them before the update will get to keep them with max promotion and equipment levels. Those who didn't will never get to use it again.
However, this vehicle still exists in the game in the form of Rocket Buggy Strike. It can also spawn as a defender unit in NPC bases or from players who own it.
The game still implies that it exists via the blast deflector's description, as well as during the campaign series "The Red Wolf."