This happens occasionally with large chops. The stump looks like Japanese maple? Sometimes caused by infection through the cut or through roots, sometimes just a response to sudden stop of sap flow. Sometimes no obvious cause.
It is possible you are just worrying too early. Sometimes buds take longer to show on older wood - fingers crossed.
If you decide to keep working with it, definitely let it grow all year and possibly 2 years to regain strength. Only reduce trunks to new leader when the leader is strong and you can be certain lots of sap flow from roots to that leader.
If no further buds emerge it is likely that some roots have/will also die as no shoots above to feed them. Also likely that the other side of that trunk will die off.
I've seen some success grafting new shoots onto stumps that have recently failed to shoot but success is not assured and not sure it would be worth the trouble.
Assuming this will be the only bud, how should I proceed?
I would probably call it quits and start over with new material but you'll need to make that call.