Your over complicating the issue.
Class Delta is defined as
Generally, that airspace from the surface to 2,500 feet above the airport elevation (charted in MSL) surrounding those airports that have an operational control tower.
If the Control Tower is not active then the class D is no longer valid; therefore that airspace and any associated stubs become whatever airspace as designated by the chart....
Using your chart - work out what altitude Class E starts at. The AIM states that Class E starts at 14,500' unless otherwise specified.
(Look over the ocean, in FL there is a line about 8nm of the coast indicating Class E begins at 1200')
Most airfields have the magenta shade around them indicating this Class E would begin at 700'.
The regulations, don't and will never show every circumstance, in the same way an instructor can't teach you everything you will ever need to know about how to fly. Some information has to be deduced given certain regulations and facts.
If your instructor doesn't know, he should be asking a colleague who does.
Note my edit on my first post RE : Class E stubs...