Axle trouble

I own a Nissan Altima 2001 and I recently brought it in for work on my break pads and rotors.

While they were working on it, the mechanics let me know that the ball bearings that are connected to the axle were both split. The mechanic suggested getting some outer cv axle boots.

Is this a necessary immediate repair or can I wait a few months before getting the repairs done?

It is better to fix it sooner. It is a gamble as to if you can wait, you may risk damage to more parts as the boots prevent dirt and debris getting into the parts and can cause harm.

If the boots split fairly recently, boot replacement could save the CV joints inside. If the grease has leaked out and water and grit gotten in, the joints are toast and a rebuilt axle(s) will have to be installed. The axles can be used for a while longer without further damage but you will start getting popping and cracking on turns. Eventually, a joint will disintegrate and the car will stop moving.

So you get to choose reliability over cheap.