The goal of BRICS is not to defeat the US and become the new world ruler, their goal is to reduce dependence on the USD. Creating a multipolar world with evenly distributed power to make the world more equal, a world not bound or oppressed by a single power. So the scenario of them turning their backs on each other and falling apart is very unlikely, they need to maintain that to keep the world multipolar and that is their goal. How can they easily give up the achievements they have worked so hard to achieve if they succeed in creating a multipolar world?
That has always been the plan. To dethrone the US as the world's leading superpower. I doubt BRICS will take the US' reign anytime soon. Especially with the EU in play. Constant geopolitical tensions in Europe will only strengthen the EU in the long run. The Ukraine war is only the beginning. Already, EU countries promised to spend 5% of their GDP for defense. Will BRICS stand a chance against the EU's military and economic might? Only time will tell.
At the time of this writing, Russia and China are the only countries capable enough to survive on their own. But I can't say the same about other countries within the bloc (BRICS). We're living in uncertain times, so anything's possible.