Looks to be a little too severe to bring all the fibres back up with moisture, which by the way, works like magic. I have revived several stocks that looked like that they had been used as cricket bats using a steam chamber.
Don't use filler, because even when finished and stained, it will visually jump right out at you no matter how well it is done.
I would probably consider a different method, which I have used in the past with good success. I believe the method is called a "Dutchman" patch repair in the woodworking and furniture world. Cut out the whole area in a very shallow (1mm deep) rectangular-ish section and inlay a piece of veneer. Sand and apply your finish. With careful selection of veneer, you won't need to stain it for a match. Sounds simple, but patience and a steady hand with a hobby knife or scalpel is needed.
Look for craft stores that sell marquetry supplies. The veneer is about 1mm thk. They will have walnut and all kinds of other colour wood sheets, plus the tools and the glue (fleabay has kits listed). It would be a half hour fix by someone skilled in the art. (Marquetry is the making of an artwork or picture out of wafer thin fitted wood veneer pieces, as opposed to paint.). Ask at the store who are their local marquetry artists, they might be open to patching it for you.
There are many pieces of old antique furniture still around decorated with marquetry, using wood, ivory, mother of pearl. Table tops can be quite durable if hardwood is used.
Anything is repairable, with time and effort (or money). I think that your stock is a project with good potential.