If you leave it in the pot the roots will expand and force the crack open further and further.
It would be good if you can get some help to extract the fatsia from the pot, give the roots several good soakings first to make the root ball a bit pliable. If it's so potbound that it's cracked the pot it's likely to be quite rigid.
I would then prune the root ball and pot up again using as much fresh compost as you can get into it - but I would pot into a plastic pot that will fit inside your decorative one.
You can then use some epoxy resin (from a hardware or DIY shop) to repair your ceramic pot, and when it's dry put the plastic pot and fatsia back inside it.
Then you and a helper can lift it out each year and repot with fresh compost, pruning the roots each time to keep it fitting inside the pot.
That's what I would do - hope that's helpful.