Its fairly average, so I probably wouldnt bother mate. At least you've got that stump to work with in a year or so.
Be prepared for a massive taproot, dig out by 300mm or so radially around the trunk and then down 300mm. Then undercut the root mass, once its out of the ground you can wash the root ball clear and assess whats worth keeping or getting rid of in the way of thick ugly roots.
Like someone mentioned before I would cut the trunkline above the nodule/bumpy section but I would also leave 50-60mm of straight trunk section as insurance in case of die back, final cut vs flush cut.
If it doesnt haver to be removed immeditaely, why not try some air layers on those strong brances Seems a shame to waste them IMO... Good prctise too...
I've tried an air layering before, but both times the tree healed the bark quicker then then roots could produce! I did try it with soil though. I might try this one with sphagnum moss and see if I get a different result
Maybe this reply is too late to save the tree but
Looking at this tree's leaves it seems to be a fruiting variety, not wild olive. Wild olives make the best bonsai as the leaves reduce. Fruiting olive leaves will remain large and not make a good bonsai.
I say give it a go. Carving will most likely be necessary to produce some taper and character, but that is no reason not to go for it - plenty of great bonsai have started the same way. You just need a bit more imagination to get the best out of it.
May have been said before, but if you do dig it up/cut it off, consider planting it at an angle, even a big one, to make it less of a pole out of the ground. May also help inspire some new thoughts on how to structure the finished tree. Good luck
And a link to mine to see what I mean is here - viewtopic.php?t=19284 . Still waiting to see if it buds. Still green when I scrape it back, so here's hoping.