The drain line coming out of the disposal must be higher than any component between it and the wall connection. Otherwise, you will always have drain water in the bottom of the disposal.
How does your 'plumber' propose to 'push' the water up to drain?
Also, that P-trap is installed backwards.

"Is this going to work?"

No.

Water does not flow uphill.

The GD will have standing water and stink to high heaven with rotting waste (and rust out very quickly).

Get a real plumber to open the wall and lower the drain.

Redid whole disposal and drain line over the weekend. Works great, quiet as hell. Had to use an inline vent, but thanks for advice.