It'll probably be an expensive repair. Take it to your local body shop and get a free estimate, but if the rust hasn't compromised the pillar's integrity yet, you should consider sanding it down, cleaning off the pillar, and then re-priming and painting the whole thing.
In fact, if that pillar is rusting, you should probably closely inspect the other pillars and the body as a whole. Grab a creeper and some floor jacks and get underneath that thing and see how the frame is doing. Inspect everything top to bottom. Pop the trunk, too; if it has a chunk of unattached carpet in the trunk, pull that up and see how the underside is doing back there. If anything's rusting, you're going to need to fix it.
If you let -any- rust go too long, you're going to be looking at one hell of a repair bill later down the road. This is especially true if you live in an area with salty air.
Am I the only one who can't take this seriously when it comes from a dude who has a lion woman as his avatar?
Yes but I provided humor in a time of great uncertainty