What are your favorite buggy-whip outlets?
If a shop cannot attract my business over the competition ... it simply cannot. if bike shops close because they are no longer profitable ... buy buggy whips?
If there is sufficient demand for bike mechanics, people will start renting small spaces and putting out online ads. If they do good work, word will spread, and they ... will be in business! And bike shops which can no longer compete with their own suppliers for bikes or with online retailers for parts, will go out of business.
It stands to reason that out of a given number of cyclists in a given region, some number will want or need the services of a mechanic/wheel builder. I can do all my own wrenching except building wheels. Some folks I used to ride with preferred to pay a mechanic for the convenience---drop the bike off, pick it up later and it is done, clean, tight, and tuned. Some folks are too busy, some simply want to spend their time doing other things. If there is a need, someone will fill it, history shows .....
Back at the turn of the 20th century, people who owned stables in-town opened garages and gas stations.
Except for some who demanded loyalty from former horse owners and whined and went broke.