The big question here is what species wood do you have and what does the figure look like at the center? It would be a shame to halve or quarter it if the figure breathtaking. Imagine it as a table with amazing figure! But it could be trash too. All burls are not created equal.
I would find any way I could to slice it dead center, where it's the widest. And I'd find someone to do it if I couldn't. But ONLY
if it was a higher quality species. If it's oak or elm or some other common species, then it's a DIY. If it's walnut, maple or cherry, I would pay someone to make that first cut if there was no way I could. A 20" cut chainsaw can reach a 40" center. If you have a forest of ebony... Call me.
There's all kinds of things that could be going on here. The rot you mentioned could have infiltrated where you can't see it. Spalted maple relies on a fungus to get its figure. And that's highly prized. Rot is another thing. No one wants that.
The stump looks like this has been dead forever. Now we're talking decay. Bugs, worms and all kinds of little creatures start feeding. And the wood becomes worthless.
So before you invest any money, know what you have. Do a small rip on the trunk with a sawzall or handsaw and find out what wood it is. If it's "pricey", then become a surgeon. If not, hack away.